Chapter 10. Evaluation: How Good Were They?

It is of little value to search for the ‘best’ A/S vessel. This leads directly to a paradox described by the Soviet naval architect Khudyakov, with at one extreme the super-battleship, the finest fighting ship of all time, but so expensive that no navy can afford more than one, and at the other the Chinese junk, cheap enough to build in numbers but having little or no operational capability.

The overall objective of the RN and its allies was the safe arrival of merchant ships and their cargoes, and the best A/S vessel was the one that used available resources most effectively to that end. Both capability, in terms of sensors and weapons, and resources change over time and led to different choices. The following paragraphs will review the decisions made at different times, both in the light of information then available and with hindsight.

Before the War

In the early 1930s there was no perceived threat in the Atlantic. The only significant submarine forces were those of the USA and France, and war with either was inconceivable. In the Pacific, Japan was increasingly hostile but it was believed (rightly) that their submarine doctrine was focused on attacking the US battlefleet.

The 1932 review of A/S capability assumed an enemy submarine force based in the North Sea. This ‘enemy’ was not named but was presumably Germany, even though that country had no submarines at that date. It was considered that few submarines would be operational in the Atlantic, because of the long passage time round the north of Scotland, and these few could be dealt with by the older destroyers and sloops. This view appears to show an underestimate of the endurance of the Type VII. Much preliminary work was put in hand for the introduction of convoys. One may also wonder how effective the sizeable U-boat fleet of 1942–3 would have been if it had been based solely in Germany. The rate at which U-boats could be built was also underestimated.

There was also an awareness of the need for faster escorts; twenty-five knots was suggested but such ships lay outside the twenty-knot limit for minor warships set by the London Treaty. Higher speed meant turbine machinery and, probably, a lighter warship structure, all making them costly and reducing the size of the manufacturing base. Recommendations for heavier armament were implemented in later sloops, as was the separation of the A/S sloop from the minesweeper role. Sensible proposals for east-coast escorts led to prototypes of both a converted commercial trawler and an Admiralty design consistent with trawler building methods. Some destroyers of the V&W classes were converted into AA ships.

It was recognised that trawlers were on the small and slow side even for coastal work and early in 1939 another review led to the Flower class corvette. As shown in chapter 2, the choice of the Flower was almost inevitable in terms of numbers needed, building slips, machinery fit, etc. Similarly, there was no choice in weapon system; the 120-series asdic and depth charge was the only system available. A design similar to the Castle but with depth charges would have been more capable and little more demanding on resources. Franklin has shown that Roskill was wrong in saying that there were no A/S convoy defence exercises between the wars,¹ but there were not many² and the lessons learnt do not seem to have reached the top.

The Admiralty faced numerous, severe threats worldwide and, not unnaturally in the lack of a perceived submarine threat, concentrated on the bigger ships that took so long to build. Battleships, aircraft carriers, cruisers and destroyers, with a very few sloops, filled every slipway in the remaining warship yards to such an extent that programmes were delayed and the sums voted by Parliament could not be spent.³ More money would not have been sufficient in itself.

The heavy workload in traditional warship yards meant that any increased number of escorts would have to be built in yards unaccustomed to warship work. Many of these yards were small and the length of their building slips limited escorts to about 240 feet. The effect of length on sea-keeping is non linear: a 240-feet ship is much better than a 200-feet one but the benefit of further increases to 280–300 feet is less. Thus the Castles had much better sea-keeping than the Flowers but were only slightly inferior to the even-longer Rivers.

Machinery production was a greater problem. Machine tools of all kinds were scarce and those that were available were often old-fashioned. Turbine blade production was limited and reduction gearing even more so. The only readily available engines were the triple-expansion, four-cylinder units based on that designed by Smith’s Dock for the Southern Pride and, though these could be built by many yards, their production still set a ceiling on numbers. This limit favoured the single-screw ships such as Flowers and Castles. Geared turbines were used in sloops and a few Rivers and Lochs. Diesels were thought unreliable at continuous power and there was little manufacturing capacity. It was also thought, probably incorrectly, that wartime crews would not be able to handle more advanced machinery. However, they had no problems with the machinery in either type of the Captain class, with only a brief conversion course. It was also thought that the simple plant would be reliable and easy to maintain. Experience with the Captains showed this idea, too, to be wrong.

Anti-submarine systems progressed quite well, considering the low priority given to ASW and the general shortage of funds. The UK electronics industry was somewhat backward. However, the RN had the best sensor in the 120 series, and the range recorder made it into the best ASW system. Lack of depth measurement was a serious drawback, not fully appreciated because of the shallow water in the main exercise area. RN submarines seem to have made little use of deep diving, so there was little input to doctrine from them. The lack of depth data combined with the time for a stern-dropped depth charge to fall to give a long dead time in which the U-boat could evade the attack. Failure to develop an ahead-firing weapon was the greatest failure of the pre-war Admiralty.

The possibility of night surface attack was appreciated and exercises had been carried out.⁴ However, until the introduction of radar, detection of a surfaced submarine was visual and, on a dark night, the range of detection was short. Numerous escorts were the only, partial solution.

Wartime Developments

Wartime developments were largely correct and timely. The Flowers were entering service from mid-summer 1940 and large numbers were on order. The Tobermory training facility would put the finishing touch to the skills of the new crews. There were fifty ex-USN destroyers coming along, although it was some time before it was realised how much work was needed to make them operational. The design of a true ocean escort, the River class, only began in November 1940 but one has to excuse this late start as the Admiralty had many things on their minds during that wild summer of 1940.

The rapid development and introduction of radar and later improvements was a success, as were the ahead-throwing weapons and their associated depth-finding asdic. It has been suggested that some of these were introduced too quickly and that a longer development time would have meant that the first sets at sea were more reliable. There is some truth in this but getting the Mk I to sea quickly was an advantage in itself and almost certainly the quickest route to a fully capable and reliable Mk II.

HMS Whimbrel. The drawings are reproduced from the official plans of Whimbrel as completed. The twin 4in guns in A, B and X position are conspicuous. Less obvious are the twin 40mm Bofors either side behind the funnel. There are single Oerlikons either side of the bridge and two twin Oerlikons in power mounts on the quarterdeck. Also on the quarterdeck are eight depth charge throwers with storage racks and two depth charge rails giving her the capability for a fourteen-charge pattern.

She has a tripod mast crowned by a HF/DF aerial and there is a lattice tower aft with 271 radar but she retains a big searchlight. The gun director has radar Type 285. Note the position of A gun; right forward, its working would be obstructed by green seas and the severe motions would degrade its accuracy. The mess decks also extend right forward causing sickness in the crew. (National Maritime Museum NPC-5344)

In the earlier years, both sides had successes in intercepting and reading the enemy’s coded signals, with the advantage swinging back and forth. Both sides were slow to realise that their messages were being read; indeed the Germans never did accept this possibility. The advantage finally settled with the Allies – Poland making valuable contributions – with heroic rescue operations, the development of shipborne HF/DF and the use of primitive computers that could read Enigma reliably and usually quickly.

How Good Were They?

The efficiency of an A/S system depends on the performance of the ship, the effectiveness of its sensors and weapons and on the skill of its crew. The economical use of manufacturing facilities is another part of the story. Finally, it must be re-emphasised that the object is the safe and timely arrival of cargoes.

Brown⁵ and Collingwood⁶ have attempted a partial answer by listing the number of U-boat kills credited to each class of A/S vessel. The crude statistics shown in table 10.1 differ slightly from those of Collingwood, probably as a result of different interpretations both of the boundary of the battle and of shared kills. The figures are very rough and ready, but they do suggest some interesting lines of thought, particularly when associated with the number of each category of escort at sea. In particular, the small number of Black Swans scored a disproportionate number of kills. In seeking an explanation, it must be noted that the majority were scored by Walker’s 2nd Escort Group.⁷ The reasons for this start with the skill and determination of Walker himself (chapter 5); in turn, this led to the ‘halo’ effect, by which if a concentration of U-boats was located, Walker’s group would be called up. There are indications that the best officers and most skilled ratings were chosen for the group. For a brief period, they were able to operate in the Bay of Biscay, working with aircraft against U-boats in transit on the surface, thanks to their heavy AA armament. The success of the group is the more remarkable in that few had Hedgehog and, until late on, none had Squid. In fact, one may query the value of the Black Swans. At £360,000, they were 50 per cent more expensive than a River; they used more skilled labour, while their geared turbines gave little advantage over a River.

whimbrel has two boiler rooms and a single engine room giving some subdivision. Note the fin stabiliser under the bridge. The Black Swans were the Rolls Royces of the Atlantic but did their heavy gun armament and turbine machinery make them more effective ASW ships? (National Maritime Museum NPC-5345)

The much greater success rate of the turbine Captains compared with the diesel ships has already been noted. Another interesting comparison is between the Flowers and the Rivers. They had the same asdic and depth charge armament, both receiving Hedgehog as available. The Rivers were faster but used two engines, a bottleneck in escort-building.

The Rivers were much more successful ‘killers’ than the Flowers but they used twice as many scarce resources without scoring twice as many kills. Collingwood’s more detailed analysis with months in commission per sinking gives 119.6 for the Flowers and 79.7 for the Rivers, a broadly similar conclusion. Both analyses use sinkings as a measure of effectiveness, which grossly underestimates the value of the Flowers, because with early, short-range asdics, two sets are better than one. Two ships are also more effective than one in keeping submarines submerged, limiting their mobility. One may conclude that in the early years of the war the Admiralty, at least, were correct in building the simpler, single-engined ships.

There are insufficient data to make a similar comparison between the Castles and the Lochs but some conclusions may be drawn. The Lochs’ double Squid was very much better than the Castles’ single, but the weapons depended on the same asdic and operational plotting equipment and hence the cost difference between a Loch and a Castle was much less than that between a Flower and a River. Based on limited data, the kill rate for the double Squid was 40 per cent compared with 23.5 per cent for the single.

Figures for the installed electrical power (see table 9.4) also reflect the lesser difference in complexity between Castle and Loch. The continued building of the Castles was fully justified as they could be built on slips too short for Lochs.

With hindsight, one may debate the value of the Towns. They required a great deal of dockyard work to make them operational in ASW. They did not enter service until spring 1941, by which date Flowers were completing in some numbers. Once in service they needed frequent maintenance and repair. They sank a fairly small number of U-boats before their early relegation to subsidiary duties. On the other hand, their appearance in some numbers implied some support from the USA and was a valuable morale booster.

Summing Up

In 1939–40, the overwhelming need was for numbers. Numerous escorts with their short-range asdics were needed to prevent submerged attack. The only sensor against surface attack at night was the eyeball Mk I. The only way to get numbers quickly was to build Flowers, short enough to fit many available slipways and driven by simple reciprocating engines.

Later, with a sufficiency of escorts, the coming of asdic Types 144 and 147, together with centimetric radar, reduced the need for numbers, and Hedgehog and Squid made a lethal combination against the older generation of U-boats. However, the future lay with aircraft.

Tailpiece. The Egyptian Tariq, formerly HMS Whimbrel of Walker’s escort group. At the time of writing (2007) it is hoped to bring her to Liverpool as a Battle of the Atlantic memorial.