10

Minor War Vessels

THE INCREASING TENSIONS of the Cold War and, in particular, the outbreak of fighting in Korea in June 1950 raised the possibility of a Soviet advance into Western Europe with British coastal waters as a battleground. Mines could be laid by aircraft, submarines, fast craft or, clandestinely, before the outbreak of war. Submarines might penetrate estuaries, possibly laying nuclear weapons, while the Soviets were developing a numerous force of fast attack vessels. To counter these threats a large number of minesweepers, seaward defence vessels and fast patrol boats were designed and built. In later years attention was concentrated on the mining threat and a smaller number of very capable vessels were built and some novel ideas were explored.

W J (Bill) Holt

The early programme was directed by W J Holt, who had been in charge of small craft design since the late 1930s.¹ He was a keen sailor and had even served briefly in a windjammer to gain experience with square rig whilst designing the non-magnetic vessel Research, which was a brigantine carrying square rig on the foremast.² During the war he led the design of the HDML, the ‘Fairmile B’ and ‘D’ classes, steam gunboats and the Camper & Nicholson MTBs, as well as MMS, etc; he also improved the structural design of the British Power Boat craft. He also built two small gunboats on the Chindwin River in Burma³ and devoted a wartime Christmas leave to a voyage in a ‘Fairmile B’ to Iceland. He was well qualified to lead the design of the next generation. One of his key assistants in postwar boats was J T (Jack) Revans, who has made an important contribution to this section.

Bildeston, a ‘Ton’ class minesweeper as originally completed with a short funnel. (P A Vicary)

Mine Counter Measures Craft (MCM)

The Tsarist navy laid the first free mines in the Baltic in the 1850s during the Crimean War⁴ and followed this with further mining success in their war with Japan in 1904–5.⁵ Soviet mining in the Second World War does not seem to have been extensive, though they did develop a magnetic mine based on the British ‘M sinker’ laid in the Dvina River in 1919. After the war there was evidence of massive preparation for mine warfare, partly confirmed during the Korean War.⁶

About 1950 British estimates were that the Soviet Union could lay 4500–6000 mines per month in British waters, and a rule of thumb held that 25–30 mines would have to be laid in order to sink one merchant ship. Losses of 50 merchant ships could be tolerated, which meant keeping the number of effective mines down to 1500–2000. On closer examination, however, the problem got worse: mines might be activated by contact, magnetic, acoustic or pressure signatures and increasingly two or three signatures had to be generated simultaneously and roughly in the right relative position. Ship-based countermeasures meant that each channel had to be swept twelve times for each mine type to ensure it was safe. Clearly a vast number of MCM vessels would be required, and most of them would have to be purpose-built with low signatures. Converted fishing vessels would only have a small part to play in a future war.

A very large number of vessels of different types was planned. The 1951 ‘War Programme’ envisaged 50 improved Algerines if the new design was not ready. By May 1954 it was planned to build 5 ocean sweepers, 167 coastal and 167 inshore sweepers, and it was always envisaged that the great majority would be laid up on completion as a war reserve. The ocean minesweeper was a pretty vessel, an updated Algerine, and the design was worked up in considerable detail and approved in January 1953.⁷ It would have displaced 1522 tons and steamed at 17.5kts free, 11.5kts towing sweeps. However, it was soon realised that a large, steel-hulled vessel had only a small role in modern mine warfare and it was cancelled in January 1955 following the Radical Review.

The Coastal Minesweeper (CMS) ‘Ton’ class

The coastal sweepers of the ‘Ton’⁸ class were much smaller, reducing pressure signature, and had non-magnetic hulls with wood planking over aluminium frames. They had a free running speed of 15kts and were intended to tow sweeps with a 9-ton pull at 12kts. At this speed the power required to tow the sweeps and pulse the magnetic sweep was five times that needed to drive the ship. This required non-magnetic Deltic diesel engines (see later), which were not ready, and early ships completed with the less powerful Mirlees engines, later replaced with Deities. Another early problem was that the aluminium frames and deck beams formed a conducting loop and when the ship rolled in the earth’s magnetic field a current was generated which produced its own magnetic signature. A complete cure was found: a sensor was installed at the top of the mast which measured the current generated and cancelled its effect using a special de-gaussing coil.⁹ The design of an all-wood CMS was in hand but dropped when the eddy current problem was solved. A minehunting variant of the CMS (Thorpe class) was designed and three were ordered, but they were cancelled before work began.

Hickleton, another CMS; this ‘Ton’ was later sold to Argentina as Neuquen. This aerial view shows the bulk and complexity of the gear required to operate wire, acoustic and magnetic sweeps.

(D K Brown collection)

The ‘Ton’ class were very successful; 118 were built for the RN, many of which were later transferred to other navies, and still more were built in France, Canada and Holland.¹⁰ In general they lasted well, though there were problems with corrosion of the aluminium frames. Those remaining in service were given a plastic sheath to protect the planking. Eighteen were later converted to mine-hunters, with an ‘active’ rudder for good manoeuvrability at low speed when using the Type 193 sonar. Some were used for trials – Highburton was used for experiments to reduce resistance by the use of long-chain molecules such as polyethylene oxide. It worked, reducing frictional resistance by some 30 per cent, but ‘polyox’ is expensive and no economic application has been found. She was also used for trials with several experimental propellers, the best of which was fitted in other hunters. Shoulton carried the first experimental pump jet units (see SSN, Chapter 9). One of the main fears was that the fine clearances between rotor and the duct would cause it to jam if debris entered the unit. However, very soon after Shoulton’s units went to sea a railway sleeper was seen to enter the pumpjet – it came out as matchsticks without causing damage!

Inshore Minesweepers (IMS)

The ‘Ham’ class inshore sweepers were even smaller (159 tons deep). The first 37 (numbered 2601–2637) had similar structure to the ‘Tons’ with aluminium frames. Since they were intended to work in very shallow water, the eddy current problem was more severe and the later 54 craft (2701–2739 and 2777–2793) were of all-wood construction with a slightly greater beam.¹¹ The ‘Hams’ were too small to take new equipments and only a few remained in service for any length of time, and these on auxiliary duties only. Mines can easily be altered to play new tricks and hence MCMV must also be adaptable. A similar aluminium-framed hull was used for the twelve ‘Ley’ class, officially referred to as IMS Type II even though they had no sweeping gear. They were intended as minehunters but there was no suitable gear and they had to deploy divers to search for mines by hand.

Cranham, an all-wood inshore minesweeper. They were good ships but too small to adapt to later sweeping gear.

(D K Brown collection)

Averley, an IMS Type II. Despite the ‘minesweeper’ designation, they carried no sweeps. They were designed to hunt for mines but the sonar intended for them failed to materialise and they could only use divers to search.

(D K Brown collection)

All these minesweepers were very seaworthy but, like all small craft, had violent motions in rough seas. Though smaller, many thought the ‘Hams’ were the better seaboats, probably because the high forecastle of the ‘Tons’ caught the wind, making them yaw.¹²The ‘Ton’ class minehunters were given Vosper fin stabilisers.¹³ One was used by the National Physical Laboratory for trials with a big fixed foil under the stem to reduce pitching. It did show some benefit but slammed violently if the foil came out of the water.¹⁴

In the light of the threat as then perceived this programme was necessary and well conducted. Most went straight into reserve as was always envisaged. Fishing craft were of little value against modern mines but their crews, still numerous, could man the ‘Tons’ and ‘Hams’. The designs were sound and many small shipyards were able to participate. There was still no answer to the pressure mine; much effort went into big plastic bags (later developed as ‘Dracones’ to carry oil – ‘the world’s largest condoms’ as they were known) or sleeves but no success was claimed, turning minds increasingly to hunting as opposed to sweeping.

The Deltic Engine

In 1943 a committee was set up under Sir Roy Fedden to advise on the development of a high power, lightweight diesel for MTBs.¹⁵ It was decided to develop the Deltic engine invented at the Admiralty Engineering Laboratory (AEL), West Drayton.¹⁶ There were three double-acting cylinders in each bank, arranged in a Δ (delta) shape. Engines were made with nine or eighteen cylinders.

A contract was first placed with the English Electric Co in August 1946 to develop and produce this remarkable engine. Development cost £1.5 million (estimate £2 million) at Napiers, starting in early 1947 (under Mr Sammons), and took about 3 years. Production engines weighed about one-fifth that of their nearest rival in the same power range. The standard engine was used in fast patrol boats and in de-rated form in the ‘Ton’ class (also railway locomotives¹⁷) where its low magnetic signature was useful. An even lower magnetic version was later used in the ‘Hunt’ class MCMV. A compound Deltic was designed with a gas turbine based on the Nene to be inserted in the centre of the delta using exhaust gases. This would have given about 6000bhp but was stopped when light coastal forces were abandoned.

Seaward Defence Boats, ‘Ford’ Class

At the time of the Korean war there was a fear that Soviet submarines might penetrate British estuaries and harbours to attack shipping or even to lay nuclear mines. As a counter to this threat a class of 20 seaward defence boats was designed by W J Holt and ordered mostly in 1951 (the last two in 1955).¹⁸ The hull form was based on the wartime steam gunboats and, though very seaworthy, they did not have bilge keels and rolled heavily.¹⁹

Shalford, the first seaward defence boat to complete. She carried a triple-barrelled Squid AS mortar aft and was very much overweight. (MoD)

They had three shafts with the main Paxman engines on the wings and a small Foden on the centre shaft. They were intended to have a single-barrelled Squid as ASW armament but this did not become available. Shalford was given a normal triple-barrelled Squid and the rest had two depth charge throwers and two racks. They also mounted a single 40mm Mark VII. Most remained in service until 1966–7.

Like many of the earlier classes described in the chapter they were a response to the Korean War. DNC department was greatly overloaded and the old rule that key design calculations should be carried out by two Assistant Constructors working independently could not be followed – indeed, neither of the calculators on the ‘Ford’ class was an Assistant Constructor. Overload was greater still in higher ranks, supervising several designs and there were numerous errors.²⁰ Even Holt was over stretched. Shalford had a design deep displacement of 108 tons and there had been 9 tons of approved additions. When inclined by the author, the displacement was 148 tons!²¹ On re-checking the original calculations there were a large number of items which had been omitted altogether – funnels, machinery seats etc.²²

Fast Patrol Boats

At the end of the war there was a perceived role for fast patrol boats, particularly in the North Sea approaches to the Baltic, which the disarmament of Germany left vulnerable to penetration by Soviet forces. Light coastal craft built in the United Kingdom during the war had a number of serious deficiencies and urgent steps were put in hand to overcome them.

The most serious problem was in engines and two approaches were tried – gas turbines and diesels, both of which would ultimately prove successful. The first attempt involved putting a Metropolitan-Vickers Gatric engine in the engine room of the Camper & Nicholson MGB 2009 driving the centre shaft. This proved the feasibility of gas turbine propulsion but showed two major problems: the need to remove salt water from the incoming air, and the external noise – 2009’s bridge was between the intakes and the funnel.²³

The Rolls Royce RM60 was a much more advanced design, using a complicated cycle to obtain good fuel economy at low speeds. Two of these engines were installed in the former steam gunboat Grey Goose and ran successfully and reliably. However, the design was too big and heavy for patrol boats and this approach died – probably to return in the Type 45 frigate.²⁴

Armament, too, had been a problem for wartime boats. The 4.5in 8cwt went to sea just after the war ended and was to be the main weapon of post-war gunboats.²⁵ It fired a 15lb shell at about 10 rounds a minute at the low velocity of 1500ft/sec. The first post-war attempt at an effective patrol boat gun, Coastal Forces System 1 (CFS 1), was abandoned as it grew – and grew.²⁶ CFS 2 (a 3.3in gun) was developed from the early Centurion tank gun firing a 20lb shell,²⁷ the mounting being fully stabilised. It went to sea in Bold Pioneer in March 1957 and, though on the heavy side,²⁸ was successful, scoring a high proportion of hits; but the RN had abandoned coastal forces in September 1957 and the project was dropped.²⁹

MGB 2009, the first gas turbine test bed. (D K Brown collection)

Grey Goose as a test bed with two RM60 gas turbines. The design was ahead of the technology of the day. (MoD)

Hull construction was tested in two early prototypes in 1946: MTB 538³⁰ was designed by Vosper using all glued plywood whilst Saunders-Roe (Saunders Engineering and Shipyard Ltd, Beaumaris) designed MTB 539 in aluminium alloy,³¹ both under H R Mason. Both provided useful lessons on what not to do and the majority of later craft had wood planking over aluminium frames.

Two long-hull prototypes (121–122ft) were designed by H R Mason to compare the merits of hard chine and round bilge hull form. Even before they went to sea, the hard chine was seen as the preferred form due to its much greater internal space. As far as is known, they never went to sea together, as the machinery was unreliable. They had two G2 gas turbines, derived from the Gatric, and two Mercedes diesels (from E-boats) – later replaced with Deities – giving a speed of about 42kts (design speed 48kts). Bold Pioneer (hard chine) went to sea in January 1953 and Bold Pathfinder in July 1953. E-boats had gained extra speed by angling their rudders and the ‘Bolds’ were given the facility to do this, but it was never tried. They were a dead end since the remaining fast patrol boats were differently derived.

Bold Pathfinder (seen here in November 1952) and Bold Pioneer were built to compare different hull forms. However, the round bilge Pathfinder and the hard chine Pioneer were never able to run in company, mainly due to unreliability, but the more spacious hull of the hard chine form was preferred. (MoD)

Bold Pioneer in 1957 with the prototype CFS2 gun mounting forward. It was very successful on trials but by then the RN no longer required fast gunboats. (World Ship Society)

The ‘Dark’ class were versatile and could be quickly adapted to various roles: as a gunboat with 4.5in and 40mm guns; as a torpedo boat with one 20mm and four tubes; as a minelayer with one 40mm and six mines; or, as demonstrated here by Dark Gladiator, as a raiding craft with a 40mm gun and dinghy.

(D K Brown collection)

Gay Centurion. The ‘Gay’ class fast patrol boats originally ran with severe stern trim, but this was cured by fitting a transom flap, which also increased their speed. The supports for the flap can be seen on the transom in this photo. (D K Brown collection)

Twelve boats of the ‘Gay’ class were ordered in 1950 following the outbreak of the Korean War, as developments of Vosper’s wartime boats, entering service in 1953. As gunboats they carried one 4.5in and a 40mm; as torpedo boats, one 40mm and two 2lin tubes. The design was by J T Revans who, on AEW advice, arranged the centre of gravity a little further aft to reduce resistance and increase speed.³² On first completing they had a top speed of about 40kts, at which they had very marked stern trim. This meant the running waterplane intersecting the bottom in the middle of the longest compartment, leading to structural damage.³³ Jack Revans suggested a flap on the transom to alter running trim, bringing the impact onto a bulkhead. Model resistance tests suggested a loss of speed of about 1.5kts but it was decided to try a flap on one boat.³⁴ On trial, speed actually increased to 44kts due to much improved propeller efficiency.³⁵ Turning at full speed, full flap and full rudder was alarming, as the heel would put the deck edge under.

The ‘Dark’ class were ordered in 1950–3 to a design initiated by Revans.³⁶ They had the same armament as the ‘Gays’ in gunboat configuration but as torpedo boats had one 40mm and four tubes. They had two 18-cylinder, opposed piston Deltic diesel engines giving 5000bhp, but which had not run when the ‘Darks’ were designed. The power available depended very much on rpm (Deltic 960rpm in ‘Darks’) and on first trials the engines locked up at 22kts and would not go further. Eventually, with a different propeller design, they made 45kts.³⁷ However, at that speed the life of the propeller was about 20 minutes increased to 20 hours after many designs had been tried. Most ‘Darks’ were paid off in 1957 when the RN gave up coastal forces.³⁸

Studies for the ultimate fast patrol boat began under Revans in early 1954, completing about 1960 after coastal forces had disbanded.³⁹ The requirement was to ‘cruise’ to the Dutch coast, fight an action and return, all under cover of darkness. This meant a sustained speed of 50kts and many wild schemes were considered including surface-piercing propellers.⁴⁰ A Deltic with a gas turbine using the exhaust arranged in the centre of the delta was under development. However, three Proteus gas turbines proved a relatively conventional solution and was the lightest arrangement for a relatively short range, high speed mission. The two ‘Brave’ class boats built to this design were to have carried the CFS 2 mount and a single 40mm as gunboats. The armament could be rapidly altered to a number of roles:- torpedo boat, one 40mm and 4 torpe-does in dropping gear; minelayer, raiding craft, etc.

Revans paid particular attention to the air intakes which, at full power, had to pass 200 tons of air per hour whilst preventing the ingress of salt particles. Earlier boats tended to come out overweight and for the ‘Braves’ a scheme was devised in which Vospers carried out the calculations which were then checked in Ship Department and matched to the design calculations. This scheme worked well and the boats completed to the design weight. Weight-saving extended to lightweight cases for standard instruments.

The design was developed by Vosper and made their designed 50kts on first trial. This reflects great credit on the company who had their own hydrodynamics department then under Hermann Rader.⁴¹ Three reduced derivatives of the Scimitar class were ordered in January 1969 as fast training boats for surface warships to practise anti-FPB action. They performed well once the right settings for their transom flap had been found.⁴² A 144ft Vosper private venture was chartered as Tenacity in 1971 and purchased in February 1973 as a fishery protection vessel.

The ‘Castle’ Class OPV – A Personal Account

Since the ‘Castle’ class were the only ships built to my design, I may perhaps be excused for giving this class more space than their humble role deserves – and writing in the first person.

In 1975 it was clear that the new international rules on Exclusive Economic Zones would need a considerable increase in the size of the RN Fishery Protection Squadron, The first step was to charter the Jura, belonging to the independent Scottish Department of Fisheries. She was found reasonably satisfactory and five (later seven) generally similar vessels of the ‘Island’ class were ordered. The following year, following another reorganisation, I found myself heading the main surface-ship design section. Our main task was to be the detail design of the Type 43 destroyer but she was still in concept and it would be at least a year before we could start. It was decided that we should design the second-generation OPV while we were waiting. This was seen very much as a training exercise; it had been 18 years since I had worked on ship design and the rest of the section had even less experience.

Lindisfarne, an ‘Island’ class offshore patrol vessel, which gave good service for many years.

(D K Brown collection)

Offshore protection differed in many respects from ‘hot’ war: 100 per cent ‘kill’ was not necessary, and we had only to catch enough to frighten other lawbreakers. The 16kt speed of the ‘Islands’ was criticised but there were very few trawlers in European waters which could exceed 12kts. Even so, a little more speed would be welcome. Fishing was virtually impossible above Sea State 5 (4m wave height) and there was little point in boarding a suspect in worse seas.⁴³

There were some preliminary studies for a slightly better ‘Island’. I maintained that it was uneconomic to devote effort and incur first-of-class costs for a ‘slight’ improvement. Unless a case could be made for a considerable improvement we should buy more ‘Islands’.⁴⁴ The argument centred on the need for a helicopter deck – the case for an embarked helicopter was soon dismissed as the Lynx cost more than the intended cost of the ship and its hangar would preclude the fitting of a landing deck large enough for bigger helicopters. There did seem a case for a big deck so that the larger Sea King and Merlin could land and refuel in rescue operations and this case was soon accepted in Whitehall, including the Treasury.⁴⁵

Jura and the ‘Islands’ were already being criticised for excessive motions and I had a literature survey carried out on the effect of motions on human behaviour.⁴⁶ The ‘Islands’ were much the same size and similar in form to the wartime ‘Flower’ class corvettes. I compared the many subjective accounts of life in the ‘Flowers’ (205ft), with the wartime ‘Castles’ (252ft) and the ‘Rivers’ (3010ft) and tentatively decided on 80m (262ft) as acceptable with a form based on First World War Admiralty ‘S’ class destroyers. In parallel with this, Dr Adrian Lloyd was using a new computer simulation to compare these Great War ships and others with my new form at various lengths. As a result of his work I decided that I could reduce the length to 75m.

This length was greater than needed from space considerations but had important advantages. The flight deck was big enough for a Merlin helicopter⁴⁷ and pitch and heave motions were much reduced. Because there was space to spare, I was able to arrange living and working spaces close to amidships where the motion was least; in particular the bridge was almost amidships.

This approach was developed in discussion with the Captain Fishery Protection, the Scottish marine superintendent and a progressive trawler owner – including a trip to sea in Cygnet – and it was rough. The new ship was to have the same engines as the ‘Islands’ but they were arranged in separate engine rooms as a precaution against flooding. The extra length brought the speed up to 19kts. A MACK with a large crow’s nest gave her a distinctive appearance carried over into the Type 24 frigate studies. We hoped to sell ‘Castles’ in the export market and produced sketches and a model showing various heavy armament fits (see Chapter 7). There were no supporting calculations but I think they were feasible though quite costly. ASWE did an interesting study on the gun for the RN vessels. The main requirement was a first-round kill at 6000 yards against a terrorist launch. The Centurion tank 105mm came out best and also, at £100,000, the cheapest. However, the Staff decided it could be improved and added 90° elevation and power loading which brought the price up to £6 million – so they got the 40mm/60 cal. Bofors.

My sketch design was widely circulated through industry, who were invited to do better or quote for my design. We had an elaborate marking frame against which submissions were judged as a result of which we chose my design to be built by Hall Russell. To our great surprise, no one challenged this choice.

Leeds Castle, a bigger offshore patrol vessel that could accept a Sea King helicopter (indeed, a Chinook has been landed on a ‘Castle’). Note the knuckle and high freeboard, with the bridge well aft. (MoD)

In early 1982 I was able to observe helicopter landing trials in Leeds Castle. These were held off the Eddystone with waves just over 4m but quite short. The test pilot was very interesting: the limiting factor was roll angle instead of vertical velocity as in a frigate. He cleared the ship for operation up to Sea State 5.1 spent much of the afternoon in the crow’s nest with Adrian Lloyd whose advice had influenced the hull form considerably. The bow shape with considerable flare and a knuckle was mine and I drew his attention to the way in which the spray sheets were thrown clear and, even in these quite severe seas, the fore deck was dry. He countered my argument by saying that it was only my heavy flare which generated the spray and if I had taken his advice there would be no spray – I still think I was right.

The design displacement was 1350 tons but we had calculated an extra deep of 1500 tons with some voids filled with oil. When the Falkland War broke out, they filled everything and they sailed at 2050 tons, serving as dispatch vessels.⁴⁸ I had given them enormous bilge keels (see photo on page 178) and during the trials we had difficulty in getting them to roll enough to test the stabiliser fins. During the war both ships lost their fins due to fatigue failure of the shafts and no one noticed the difference. Reports from sea after the war were very enthusiastic.⁴⁹ I suspect from measured motions that the COs on the bridge, near amidships, exaggerated their good behaviour.

The Hydrofoil Speedy

The RN had displayed interest in hydrofoils since the early 1920s but all projects had been unsuccessful.⁵⁰ By 1978 Boeing had published papers on the use of hydrofoils in the fishery-protection role and the US Coastguard were operating the Grumman Flagstaff. OPV studies showed that there was merit in hydrofoils in the role if they did not cost too much – implying an adaptation of an existing craft. The UK were also involved in a NATO group studying ASW hydrofoils using towed array (700–1300 tons). Put together, there was a good case for purchasing such a craft as a demonstrator. The Boeing ‘Jetfoil’ was the only craft available within the timescale which, for financial reasons, was very tight.⁵¹ The next year Speedy, with the author on board, was able to run speed trials in Puget Sound at 43kts.⁵² Boeings delivered her as a bare hull and machinery and she was fitted out by Vosper Thornycroft as sub-contractor to Boeing. On completion, she commenced a lengthy trials programme, which was curtailed by the Nott Defence Review. The author’s summing-up was: ‘She achieved all we promised and most of what we hoped for.’

The Second Generation MCMV

Round about 1960 a committee was set up to consider the next generation of MCM craft. The team was led by the Admiralty Research Laboratory, Teddington, and was to be a very wide-ranging study. When the team came to AEW, Haslar, they were clearly expecting a very conventional approach, but had a surprise.⁵³ Our choice was a catamaran, chosen to provide a wide working deck with plenty of space for additional equipment. First choice for propulsion was two very large air propellers (helicopter rotors on end) above the sweep deck to shield the airborne noise. Big outboard motors would be fitted for cruising in safe waters. Our second choice was still a catamaran but with a steam reciprocating engine driving a paddle wheel between the hulls. This was based on noise trials with a Dockyard steam paddle tug dating from about 1890 which proved very quiet at important frequencies. Other establishments came up with equally far out – but promising – ideas.

There was a debate central to the whole programme as to whether the ‘vessels’ should be combined hunter/sweeper or whether two types were needed. Eventually the decision came down in favour of the combined vessel, mostly on manpower grounds, though direct cost also favoured the combined vessel. The runner-up was a bottom-crawling, submarine ‘tank’.

The Development of the ‘Hunt’ Class

Even the decision that the next MCMV would be a conventional combined hunter/sweeper left many choices free. One in particular caused a great deal of debate – should the hull be laminated wood or glass reinforced plastic (GRP)?⁵⁴ Full-scale test sections of both forms of construction were made and tested by underwater explosions. Initially neither did well – one GRP section was said to look like Shredded Wheat after the bang. With experience, both types were made to perform well, though by that time there was so much plastic glue in the ‘wood’ version that it was described as Wood Reinforced Plastic!

Speedy, a Boeing Jetfoil, seen after completion in the UK. The author carried out preliminary trials in Puget Sound during which 50mph was reached.

(D K Brown collection)

There were still many options⁵⁵ – what sort of glass fibre and which resin? Sandwich construction, framed or monocoque? At that time GRP was seen as a bad fire risk but by the right choice of material this was completely changed. Ledbury had an oil fire which burnt at about 800°C for 3 hours with comparatively slight damage to the structure.⁵⁶ The other material problem was water absorption which was also overcome after numerous and prolonged tests.

The first GRP structure tried consisted of a sandwich with two GRP skins enclosing a core of small GRP ‘boxes’, and it failed under severe shock. Better sandwiches have been tried but the problem is that after an explosion or fire there is no way of checking if the joint from skin to core is still sound. The decision was made to use a single skin with frames and this has been adopted in all three generations of RN MCMVs. Initially, there was a tendency for the frames to tear away from the skin under explosive loading and the ‘Hunt’ class frames are bolted to the skin. More recent resins have obviated the need for this complication in the Sandowns. The alternative of a thick monocoque has been used successfully but it seems to have no advantage over the well proven British design. In the mid-1980s a GRP hull was designed in MoD and built by the Halmatic company using a single skin stiffened by longitudinal corrugations instead of frames. It proved cheap to build and did well in both static strength test and in explosions, but the idea was too late for the Sundown class.⁵⁷

Wilton⁵⁸

It was then decided to build a prototype vessel to prove this new material under service conditions. The prototype was to be an exact replica of a ‘Ton’ class. The Derriton was scrapped and all her machinery, equipment, etc was to be transferred to the new vessel, Wilton. She was to complete as the world’s largest ‘plastic’ ship. The main hull had a surface area of 10,000ft², with another 15,000ft² of decks and bulkheads and a GRP superstructure, a total of 130 tons of GRP using 900,000ft² of glass cloth. (Wilton’s life expectancy has been quoted as 60 years and she is halfway there. She should be preserved as the world’s first plastic ship.)

Though GRP is strong in tension it lacks stiffness and such structures can be prone to buckle. Experience from earlier tests had shown how this could be allowed for in the design. This led to a very lightly stressed structure – maximum stress about 1 ton/in². Vosper Thornycroft paid great attention to the training of the workforce and to their safety. The solvent Styrene is both a fire and health hazard and levels had to be carefully controlled and monitored. (A few people could not tolerate it at all.) Glass fibres can cause dermatitis, but with the care taken actual problems have been very rare.

There were no serious difficulties in building Wilton and her long service life has been relatively trouble-free. There were early problems with corrosion of underwater fittings and with painting but these were soon overcome with more suitable materials. She was, however, accident prone, with two collisions and a small fire in early years. One collision removed her bow but her mould had not been destroyed and a new section was moulded and glued in place, demonstrating that GRP is easy to repair. GRP is damaged by most paint removers so a barrier coat of epoxy polyamide was applied over the GRP before normal paints were applied.

Wilton, the first GRP warship. After a long career, she is now a floating club house. (MoD)

The ‘Hunt’ class Atherstone. Strict controls on magnetic signature meant that there was little weight growth during the building and consequently the ships are virtually indistinguishable one from the other. (Vosper)

GRP construction is not cheap – at the time Wilton was built (completed 1973) it cost about £5500 per ton compared with £1500 for a steel hull, equating to about £0.5 million in a ship. However, this was the prototype and the cost was halved during the ‘Hunt’ programme.

The Learning Curve

It is well known that the unit cost of the later units of a run of similar artefacts will reduce considerably as a result of learning by both management and workforce, including the introduction of short cuts, and also due to the wider distribution of fixed costs such as tooling. This has been quantified as ‘Caquot’s Law’ – the direct production cost of a mass-produced article varies in inverse proportion to the fourth root of the number of units in the production run.

This rule applied very well to mass-produced Second World War merchant ships of the ‘Liberty’, ‘Victory’ and the ‘T2’ tanker classes. It is also followed closely by the Vosper-built ships of the ‘Hunt’ class in which the man hours required for the eleventh vessel were little more than half that required for the first ship. Nuclear submarines built at Barrow and Leanders built at Yarrows show significant reductions in cost, though at a slower rate.⁵⁹

Note that savings from the learning curve occur only if there is a run of ships from the same builder and hence one cannot normally have these savings as well as those from competition; it is one or the other unless the total order is large enough to split into two equal and numerous parts. Benefits from learning are not automatic but require a determined effort from management and workforce to ‘learn’.

The ‘Hunt’ class

The ‘Hunts’ were to be combined sweepers and hunters. As a sweeper, they towed an updated Oropesa sweep for moored mines, and influence sweeps for magnetic and acoustic mines. This implied some dozen bits of ‘ironmongery’ – floats, diverters, generators, monitors, etc – all with wires and cables needing big winches and reels on board. At sweeping speed the propellers had to generate several tons of towing force to pull all this gear. The large, slow-running propellers were as quiet as possible but the flow in the towing condition was very different – and more difficult – from that in the free-running or hunting mode.

As hunters they would locate a mine with the hull-mounted Type 193M sonar. If a suspect object was detected, the ship would circle round it the better to identify it (the shadow was often useful). If it was a likely mine, a remote-controlled micro submarine (the French PAP 104) would be sent down for a closer look with closed-circuit television. If it was a probable mine the PAP could drop a demolition charge and, once the PAP was safely out of the way, the charge – and mine – could be exploded.

Weight was strictly controlled to keep the pressure signature low and an early weight-reduction programme took 70 tons off the early design figure, though a small part of the ‘saving’ proved impracticable in build.⁶⁰ All forms of magnetic material were limited but some degaussing was still needed. The main engines and the pulse generator were low-magnetic 9-cylinder Deitics and there were three Foden generators. The engines and generators were mounted on four rafts suspended from hull brackets above the waterline. The rafts were a very clever item of GRP design by Slingsby, the glider builders. Under ultra quiet conditions the propellers were turned by hydraulic motors working off the auxiliary engine. A bow thruster (another special, quiet design) and two big rudders gave excellent manoeuvrability.

A full scale mock-up was built at Woolston and, once it had been approved by designers and operators, very few changes were permitted. A machinery unit was assembled on shore and tested. The design was produced in association with Vosper Thornycroft, who prepared the 7000 drawings (+ 4000 equipment drawings). Thirteen ships were completed between 1978 and 1988, two by Yarrows, the rest by VT. The first, Brecon, cost £24 million but the last required only half the man-hours, the effect on cost being concealed by inflation. There were problems but all were overcome. Since the hull was non-conducting an elaborate electrical earthing system was needed – as was a lightning conductor! Electronic spaces in GRP were transparent to radio frequencies and needed screening. The gun was intended for peacetime patrol work and would be removed in war to reduce magnetic signature.⁶¹

Hovercraft are almost immune from mine explosions, as demonstrated by this trial against an elderly SRN-3 craft (just visible, bottom right). After the plume fell she was reboarded and her engines, radar and radio still worked. (BHC)

An impression of the SRN-4 cross-channel ferry as an MCMV. She could carry all the kit of a ‘Hunt’ class and operate at least to the same speeds – but transit would be at 65kts. (D K Brown collection)

When Brecon went to sea there were numerous com plaints of seasickness; model tests and computer simulations were rechecked but no explanation was found. There were no such complaints from the second ship, nor from Brecon’s second crew when she recommissioned. A naval doctor found the explanation – Brecon’s first crew had all complained of sickness on their previous ships!

By the end of the Gulf War in 1991 the minehunting system was fairly old but worked very well. The five British ‘Hunts’ dealt with the sophisticated mines leaving the numerous moored mines to our allies.⁶² There is a story which deserves to be better known – when the allied fleet returned to Kuwait City led by a US battleship and overwhelmingly USN, the American admiral signalled to the five little ‘Hunts’: ‘You’ve led us in war, now lead us into harbour in peace.’

A Forward Support Unit was installed in a number of containers which could be taken to a convenient location for a particular operation. During the 1991 War the FSU containers were carried in the LSL Sir Galahad.⁶³ A Vosper hovercraft was purchased and adapted to carry spare acoustic sweeps from the FSU to craft at sea but was scrapped under the Nott Review before the scheme could be tried.

MCM Hovercraft, MCM(H)⁶⁴

The Inter-Service Hovercraft Unit was set up in 1961, only two years after the historic first crossing of the Channel by SRN-1. By the mid-1970s attention was centred on the role of hovercraft in MCM. When the author took over in 1976 most aspects had been proved in full-scale trials and outline drawings were available for an MCM(H) based closely on the commercial cross-channel car ferries, the SRN-4. This craft could carry and operate all the ‘Hunt’ class sweeps, up to the same speed and in the same sea states at least.

The SRN-4 hovercraft in commercial form met the noise target and was close to the magnetic signature (it would have been fully met with small changes). The pressure signature was low but unusual – there was even a possibility of using it to clear pressure mines. The noise target was met while turning – some 10 per cent of the time – unlike the ‘Hunts’. All these signature levels were inherent in the air cushion and did not need expensive equipment or noise mounting, and there was no need for frequent monitoring. Mine explosions were tried against the ageing SRN-3, which withstood seven 1100lb charges with the last just clear of the skirt. When she re-emerged from the spray she was still hovering and the commercial radar and radio were still working.

The Utility Minehunter aimed at one-third the cost of a ‘Hunt’ class. The diesel generators, operations room and sonars were in containers. The author considers this the design of which he is the most proud.

(Artist’s impression and profile MoD)

The pylon-mounted propellers of the SRN-4 gave her exceptional manoeuvrability and track keeping – better than a ‘Hunt’ in severe wind and waves. It was proved that a hovercraft could use a Type 193M sonar at least as well as a ‘Hunt’, though the MCM(H) would normally use twin towed, side scan sonars to locate mines. The hovercraft could deploy at 70kts.⁶⁵ In war, a hovercraft unit could operate from any beach using a containerised support unit (though the noise made them unwelcome neighbours in peacetime). The craft would have had a built-in jacking system for maintenance.

Costing a hovercraft unit proved difficult; they were much cheaper to build than ‘Hunts’ but more expensive to run. Life costing over 20 years is not easy and we tried various approaches, all of which showed a clear cost advantage for the hovercraft. (We also costed USN style helicopters but they were incredibly expensive.) From the Director General (Daniel) downwards, Ship Department was enthusiastic but the Staff and sonar teams were opposed. The argument was fought without publicity but it was prolonged and bitter. It is one of the author’s major professional regrets that the RN does not have an MCM Hovercraft unit. I was sent to support sales drives in Teheran, Kuala Lumpur and Bangkok but, without RN purchases, customers were not convinced.

A very good case was put forward by the Hydrographer for a HM-5 side-wall hovercraft to be used as a survey vessel in the Thames estuary, but this was another victim of Nott.

ERMISS, the Explosion Resistant Multi-Influence Sweep System

There was increasing concern that future mines would be camouflaged (disguised as rocks) or even buried beneath the seabed, making hunting very difficult indeed. ERMISS was seen as a possible solution; originally devised in the USA it was backed by other nations in NATO – France, UK, Netherlands and Germany (NATO PG 14). The principle was entirely different from other forms of MCMV in that the vessel should pass through a minefield exploding mines underneath itself without serious damage.⁶⁶

The vessel consisted of an inflatable, peripheral rubber tube like an inflatable dinghy but much bigger and self-propelled (up to 18,000 tons was contemplated). This supported a raft clear of the water in the form of an egg box. Each cell was sealed at the bottom with a flexible diaphragm and filled with water to a carefully tuned depth. The air space between the raft and the sea was slightly pressurised and, though this provided some lift, ERMISS was not a hovercraft. It was hoped that variations in air pressure would tune the signature. Noise and magnetic generators would be installed so that ERMISS could represent a wide range of likely targets.

A preliminary full-scale test of a section of the inflatable structure showed that it could resist the explosion of a mine underneath. Negotiations to set up the project were lengthy, and when the author took over ERMISS was given a 5 per cent chance of success, but there was nothing else in sight that could do the job and the UK contribution was small in the development phase. It was an interesting task and very instructive on the problems and rewards of an international project.⁶⁷ Progress was made and when the author in turn handed over the project he was able to tell his successor that the chance of success had risen to 10 per cent. The test section failed in the final explosion and the project was abandoned. (In the author’s view it could have been made to work but only at great expense and other ways of dealing with the problems were in sight.)

The Utility Minehunter (UMH)

Towards the end of the 1970s, Jack Daniel (DG Ships) realised that, though the ‘Hunts’ were very capable vessels, their cost meant that the RN could never afford enough of them. He suggested building some cheap MCMVs which would complement the ‘Hunts’, doing the easier tasks whilst the ‘Hunts’ tackled the more difficult aspects. John Coates, then Chief Naval Architect, chaired two exciting meetings during which we developed Daniel’s ideas in brain-storming fashion (the author was head of forward design). It was soon apparent that a cheap sweeper was not possible as the towing pull was so great that powerful engines and hence a big hull was needed. However, a cheap hunter seemed possible.

Our principle was the well-known engineering rule ‘If in doubt, leave it out’. Fairly soon, we devised a scheme in which simple, bare GRP hulls would be built in a single yard not engaged in the ‘Hunt’ class programme. There would be three diesel generators, each in a standard ISO container, fitted out in a factory, on the upper deck. The operations room and annex were also containerised and assembled and tested in a factory. The sonar gear could be fitted in a box that was non-standard but could be accepted by ordinary container handling gear. Putting these items together was well within the capability of a big yacht builder – we even proposed to give them a pre-cut wiring harness. The equipment would be the well-tried Type 193M sonar and PAP submarine for disposal. Putting everything on the upper deck led to stability problems and she ended much fatter than the much-touted ‘fat frigate’.

Our operational research mathematician, Ian Smith, had examined the original basis for the ‘Hunt’ class requirements and found the very stringent signature levels derived from the need to sweep close up to an invasion beach. Such operations were now unlikely and levels were relaxed a little with some limitation on minimum operating depth of water. This enabled us to use commercial equipment for some purposes. Our target was one-third the cost of a ‘Hunt’ and probably could have been achieved. The preliminary report was accepted by Daniel and passed to the staff.⁶⁸

Needless to say it was ‘improved’ in Whitehall, with a new and very expensive sonar, a new gun and so on. The cheap minehunter was dead and Sandown was conceived. The UMH was and remains the author’s favourite design and it made a lot of sense at the time. In the twenty-first century when the RN is cutting down on MCMV numbers, Sandown, a most capable ship, makes sense.

The Sandown Class

Though the new vessels were inspired by the utility minehunter, there was little in common except they were hunters with no sweeping gear.⁶⁹ Possible contenders were a new design, a single role ‘Hunt’, the Tripartite MCMV, or a hovercraft. Possible builders were invited to comment on the draft Staff Target at an early stage.⁷⁰ It was decided to go ahead with a new design led by Vosper Thornycroft, directed by Bernard Ramsay in Ship Department.

There was another review of the material and design of the hull structure, shown in the table.⁷¹

Matrices such as these are very sensitive to input changes. At a meeting with the German Navy they used much the same headings to reject GRP and chose non-magnetic steel.⁷² They had a lot of experience with the steel and saw first cost as low whereas, lacking experience in GRP, they thought it expensive, while the British view was the opposite.

The signature levels for a hunter are less stringent than for a sweeper – towing a sweep the ship goes over the mine first! – but were still severe. Six different materials including various form of GRP, wood, steel, reinforced cement etc were considered under six headings such as first cost, ease of maintenance, durability, fire resistance etc. A single skin GRP structure much as the ‘Hunts’ was the clear winner.⁷³ Some improvements were possible due to new materials and techniques. For example, compliant resins meant that it was no longer necessary to bolt the frames to the skin.

Very high standards of manoeuvrability were required, which could most easily be met by twin Voith-Schneider cycloidal propellers. Commercial versions had high levels of both mechanical and hydrodynamic noise, but a lengthy programme involving MoD research establishments and the manufacturer brought the signature to an acceptable level. Bow thrusters were also fitted and a computer ship control system was installed to operate the complex propulsion/manoeuvring equipment. Accommodation was grouped amidships in the low-motion area and also to protect the crew from the explosion of contact mines. This led to a freeboard forward which was much less in relation to the length than in the ‘Tons’ and ‘Hunts’.⁷⁴ The Type 2093 sonar was a new variable depth set. They mounted the new 30mm gun.

The first of class was ordered in 1985 and launched in April 1988. Vospers had devised a novel scheme of outfitting sections of GRP structure before assembly, but despite this they were expensive ships, very much the same as the ‘Hunts’, mainly due to the high cost of the sonar. At the launch of Sandown the managing director (Peter Usher) boasted that she was not only their first computer designed ship but also the first in which all the production scheduling – the arrival of each item in the assembly shop just before it was needed – was also computerised.⁷⁵ It is understood that they have proved very successful in service. Twelve have been ordered, as well as three for Saudi Arabia, while Spain is building a modified version. The mine threat remains serious.

EDATS (Extra Deep Armed Team Sweep)

During the early 1970s NATO became aware of the Soviet ‘Cluster Bay’ mines.⁷⁶ These were moored close to the bottom and on detecting a submarine would fire a rocket-propelled charge at it. A special sweep was devised which would follow the bottom contours and use explosive cutters to cut the moorings of such mines. Since the mine was only activated by submarines, quite simple sweepers could be used.

The principle was proved on chartered trawlers in 1978, and in 1980 the twelve ‘River’ class ships were ordered. They were designed and built by Richards (Lowestoft), based on an oil rig support vessel with considerable input from Ship Dept. In peacetime they have been used as RNR training vessels.

Sandown was originally seen as much cheaper than a ‘Hunt’, but the class acquired more and more advanced equipment and ended up at about the same cost, although for a much more capable hunter. Here the name ship uses her Voith Schneider propulsors to turn at rest. (Mike Lennon)

¹ D K Brown, A Century of Naval Construction (London 1983).

² J Maber. ‘The “Nearly Non-Magnetic” Ship’, Journal of Naval Engineering 25/3 (June 1980).

³ W G S Penman and D K Brown, ‘The Chindwin Flotilla’, Warship 19(1981).

⁴ B Greenhill and A Giffard. The British Assault on Finland (London 1988).

⁵ D K Brown, ‘The Russo-Japanese War. Technical Lessons as Perceived by the Royal Navy’, Warship 1996.

⁶ C A Utz, Assault from the Sea – the Amphibious Landing at Inchon (Naval Historical Center, Washington 1994).

⁷ Most of the calculations were carried out by a Chief Draughtsman, Steane; my memory is that he filled nine workbooks. Drawing in E Grove, Vanguard to Trident. Planned numbers varied. Up to 21 at time of cancellation; replaced by 20 CMS, later also cancelled (ADM 205/97, PRO).

⁸ They originally were to have had insect names preceded by a colour adjective – red, blue green, golden – denoting variations in the equipment fitted. Imagine serving in Green Centipede! Mountbatten stopped this nonsense in 1952.

⁹ The trials involved forced rolling of a vessel in dock, the roll being induced by men running from side to side; a procedure devised by William Froude in the 1870s.

¹⁰ The author inclined several, see Appendix 4.

¹¹ The original IMS and the IMS Type 2 came out much overweight and with poor stability, requiring ballast.

¹² The papers were dug out during debate on the configuration of the Sandowns.

¹³ I doubt if these made much difference.

¹⁴ The fin drew air down which entered the cooling water inlets, stopping the engines.

¹⁵ ADM 167/135 (PRO).

¹⁶ AEL developed the ASR 1 diesel for bigger ships at much the same time. It is remarkable that for all the problems of commercial diesels, a government laboratory produced two fine engines. The cylinder design but not the Deltic configuration (due to an E-in-C draughtsman, H Penwarden) is said to have derived from the Junkers aircraft diesel. See Le Bailly, From Fisher to the Falklands (London 1991), p80.

¹⁷ K Hill, ‘The “Deltic Revolution” 40 years on’, Backtrack (Feb 2001).

¹⁸ It would seem that 24 were ordered and 20 completed (see Conway’s All the World’s Fighting Ships 1947–1995, p536). One uncompleted hull was used, upside down, as an office in Chatham Dockyard.

¹⁹ On first going to sea in rough weather the CO of Shalford complained that his ship was unsafe. A very experienced assistant was sent who had commanded a Fairmile ‘B’ in the war. He found that no one in Shalford had been to sea in anything smaller than a Daring and that Shalford was quite normal but needed many more hand holds.

²⁰ Controller reported the problem with many examples in ADM 167/143 (PRO). Errors were made in relation to the ‘Ham’ class inshore minesweepers, and all frigates before the Type 81, including a serious error with the Whitby, only corrected at the last moment.

²¹ Figures from memory – they were seared into my brain and I think they are about right.

²² For this reason, I tend to prefer scaling from a reliable type ship to direct calculation as there is much less chance of omissions. Certainly I would be worried if the two approaches gave a markedly different answer.

²³ C E Preston, Power for the Fleet (Eton 1982), pl1: ‘a mixture of a scream, a roar and a whine with the scream predominating’.

²⁴ Grey Goose was still afloat in 2001.

²⁵ MTBs 528 and 5008 appeared at York in September 1946 with this enormous gun. It was based on an army howitzer, designed by Major Jeffris. Its HE shell was devastating against light structure but with a high trajectory and unstabilised mount hitting was difficult.

²⁶ It was proposed to fit it in the liner Queen Mary.

²⁷ The complete round weighed 30lbs, the heaviest which could be handled under the high accelerations of an FPB.

²⁸ The weight included a 5cwt balance weight.

²⁹ A variant was considered for the ‘Castle’ class OPV.

³⁰ Originally the last of the 1944 class but in late 1944 was set aside for experimental work.

³¹ Probably an Admiralty hull form.

³² The whole section on FPBs owes much to the memories of J T Revans passed in a private letter to the author in July 2001. Geoff Hudson has also helped considerably.

³³ The author’s very first job was to try, unsuccessfully, to design suitable stiffening.

³⁴ This trial flap was made by the shipwrights at Hornet, the Coastal Forces base. Dr Gawn (AEW) was concerned about the dangers of porpoising, but this did not occur.

³⁵ It took about 20 years for me to convince people that a flap would help at least some frigates. Eventually, trials on Avenger gave an improvement of about 1.5kts (Chapter 7).

³⁶ Nineteen were ordered, including Dark Scout, but Dark Horseman was cancelled in November 1957 after launch. Dark Scout was of all aluminium construction.

³⁷ One of the best propellers tried was a slightly modified E-boat propeller.

³⁸ Mainly because a re-arming German Navy was taking over the Baltic approaches.

³⁹ J T Revans & Cdr A A C Gentry, ‘The “Brave” Class Fast Patrol Boats’, Trans RINA (1960), p367.

⁴⁰ There were even thoughts of a stern paddle wheel.

⁴¹ At 50kts the whole back of the propeller is covered in a cavitation bubble, making it a slightly easier design problem than 40–45kts with only partial cavitation. Even so, it was a great achievement by Vospers and Rader.

⁴² Revans had to be ‘borrowed’ from his new job to get the settings right.

⁴³ I did a boarding in about that sea state.

⁴⁴ We also looked at hovercraft, airships and hydrofoils, the latter leading to the purchase of Speedy.

⁴⁵ A very effective commander in Director of Operational Requirements Sea helped greatly.

⁴⁶ See Chapter 12.

⁴⁷ A Chinook landed on during the Falklands War.

⁴⁸ Displacements from memory.

⁴⁹ D K Brown, ‘Service experience with the “Castle” class’, The Naval Architect (Sept 1983), p255. Also subsequent correspondence.

⁵⁰ D K Brown, ‘Historic Hydrofoils of the RN’, High Speed Surface Craft (April 1961).

⁵¹ Grumman could not meet our very tight timescale and at that time Rodriguez did not have a craft big enough.

⁵² She was accepted with the speed reading 50 mph in a specially lightened condition.

⁵³ At that date AEW had a quite unjustified reputation for being old-fashioned – just as we led the world in topics such as noise-reduced propellers, submarine control etc.

⁵⁴ Note that ‘Fibreglass’ is one company’s trade name and best avoided.

⁵⁵ D Henton, ‘Glass Reinforced Plastics in the Royal Navy’, Trans RINA (1967).

⁵⁶ We cut out many sections for examination. The bulkheads and deck were such good insulators that they were barely warm on the side remote from the fire.

⁵⁷ I think it was sold and became a houseboat.

⁵⁸ R H Dixon, B W Ramsay & P J Usher. ‘Design and Build of the GRP Hull of HMS Wilton’, RINA Symposium on GRP Ship Construction, London 1972. The other papers in this volume are relevant.

⁵⁹ Caquot gives an exponent of 0.25; Barrow SSN 0.32; Yarrow’s Leanders 0.13. The two latter figures are a rough guide only: the SSN were not identical and the Leanders were not from a single large order. The twelfth Sandown took about 55 per cent of the man-hours of the first.

⁶⁰ A J Harris, ‘The “Hunt” Class Mine Counter Measures Vessels’, Trans RINA (1980), p485.

⁶¹ In preparing for the 1991 Gulf War extra guns were fitted. However, on arrival, they found that the use of weapons by ships without linked operations rooms was forbidden!

⁶² D K Brown, ‘Damn the Mines!’, USNI Proceedings (March 1992). The author was in Dulverton.

⁶³ They supported the USN vessels as well as the five ‘Hunts’.

⁶⁴ C M Plumb & D K Brown, ‘Hovercraft in Mine Countermeasures’, High Speed Surface Craft Conference, Brighton 1980.

⁶⁵ On a long voyage frequent refuelling would be needed, reducing the transit speed to a mere 45kts, or three times that of a ‘Hunt’.

⁶⁶ H W Groning, ‘A New Concept in Mine Countermeasures’, International Defence Review (1979).

⁶⁷ Most of the other national team leaders were brilliant and likeable; three reached the top of their profession. The social life was splendid.

⁶⁸ I received the best compliment of my career. Daniel said, ‘Not a bit what I wanted but I rather like it.’

⁶⁹ The Saudi version had a light sweep.

⁷⁰ I particularly liked the British Hovercraft Corporation comment that they could not meet the endurance at 12kts as requested but could meet it at 50kts.

⁷¹ A Bunney, ‘The Application of GRP to Ship Construction’, RINA Junior (1986).

⁷² A special alloy with very low magnetic properties.

⁷³ I am not a great believer in these matrix solutions. They are easy to manipulate so as to come to the pre-conceived answer or, if they do not, are ditched. It is well worth while going through the motions as it may expose one’s own prejudices but throw away the answer. D K Brown, ‘HMS Sandown – the third generation’, Warship Technology 8(RINA 1989).

⁷⁴ The author was initially unhappy with this but was eventually convinced by the old paper comparing the ‘Hams’ and ‘Tons’ mentioned earlier.

⁷⁵ A remark somewhat weakened by a comment from the technical director’s daughter: ‘My daddy designed that ship and he doesn’t know anything about computers.’

⁷⁶ N Friedman, Naval Weapon Systems (Annapolis 1989), p450.