The transfer of A-4 (V-2) rocket testing and manufacture from the Baltic to Blizna and the Harz Mountains did not end secret weapon development at Peenemünde. The flying-bomb (FZG-76 or Fi.103) installation at Peenemünde West had not been touched by the raid of 17–18 August. Tests of the pilotless aircraft continued, yielding intelligence data—collected by both neutral Swedes and combatant Danes and Poles—which reached London in increasing volume during the last months of 1943 and the spring of 1944. That was inevitable. Unlike the rocket, whose launch could be concealed, which flew beyond the speed of sound and which disintegrated on impact, the flying bomb gave all too much evidence of its existence. Flying as it did at subsonic speed and low altitude, emitting both a highly visible jet flame from its engine and a distinctive interrupted pulse beat (hence “doodle bug,” as it came to be called by Londoners when it began to bombard their city after 13 June 1944), the flying bomb attracted widespread attention in the Baltic lands it passed and in Poland, where its longer flights sometimes ended. Because its terminal speed was low, it also tended to leave plentiful evidence at its crash site, if a warhead were not fitted. Indeed, the first descriptive report of a “bomb with wings” to reach England came from the Polish intelligence network in the Paris area; large numbers of Poles had settled in France after the First World War, originally to work as coal miners.19 Some heard the news from Poland and passed it to London, where it was received in April 1943. On 23 June, SIS (MI6) received another report, from a Luxemburger employed at Peenemünde, which “described a cigar-shaped missile fired from a cubical contrivance [and] gave its range as 150 km for certain but 250 km was possible.” A week or two later, SIS received, via Switzerland, a “very dirty ragged sketch plan” of the launching of a pilotless aircraft from the same Luxemburger, who had managed to escape from the Peenemünde forced labour camp (thereby probably saving his own life).20 SIS later informed its Swiss office that the sketch “had been invaluable for the light it threw on what was going on at Peenemünde.”21
It is significant that these reports from within occupied Europe came from non-British sources. One of the most remarkable revelations of Hinsley’s exhaustive work comes on line 8 of page 125 in Volume 2, which reads, “Even had it been practicable to maintain agents in Germany . . .” This is an extraordinary admission, for it means that although Britain had two large foreign espionage organisations at work during the war years, the long-established Secret Intelligence Service (SIS or MI6) and the war-raised Special Operations Executive (SOE, devoted to subversion as well as intelligence gathering), it had no directly employed agents inside the Reich itself. Human intelligence (humint) came either from Germans, infinitesimal in number, or from foreigners working in or able to travel to Germany, particularly Poles and Czechs. Despite being occupied in 1938 and 1939, Czechoslovakia and Poland had been able to sustain, through their governments-in-exile in Britain, intelligence services inside Nazi Europe, to gather information, to run couriers and to transmit to London. Not so Britain. Its networks inside Germany—following the disastrous Venlo incident of 9 November 1939, when the Germans entrapped two Secret Intelligence Service officers in Belgium—were “rolled up,” as those in Austria had been after the Anschluss of 1939; its network in Holland had been penetrated and compromised as early as 1935.22 Thus, by a curious reversal of relationships, Britain became the intelligence client of two politically inert governments, the Czech and Polish, exiled to London, dependent on them for certain important sorts of signal communications inside Europe, as well as for what humint they could gather. The Secret Intelligence Service did have one presumably German contact inside the Waffenamt, the German army’s equipment office, perhaps an unwitting informer, from whom some information was passed to London through Switzerland.23 Intelligence was also obtained more directly from the Norwegians, who were able to sustain direct sea communications with Scotland, from the Danes and from the Dutch; the SOE networks in Holland were, however, deeply penetrated by the German Abwehr. The only regular and reliable foreign intelligence from northern Europe came via the British embassy in Stockholm, but later in the war. In the earlier stages Sweden was, as it had been throughout the First World War, distinctly pro-German.
Nevertheless, humint played a significantly greater part in the identification of the V-weapons than it did in any other sector of the British intelligence war against Germany, the result of the intrinsic visibility of the object of interest, notably the flying bomb, and of Germany’s dependence on foreign workers, who were inquisitive, observant and pro-Allied, often very courageously so. What today would be called “national technical means”—then taking the form of photographic reconnaissance—also played a very important part, and, marginally but significantly, Enigma again. The Luftwaffe’s wretchedly poor signals security allowed Bletchley to eavesdrop on the transmissions of a specialist regiment whose duty was to monitor secret weapon flights.
From July 1943 onwards, the intelligence intake began to refer more frequently to a pilotless aircraft, forcing London to accept that both a rocket and a flying bomb were under development simultaneously; a report from an embassy stated so explicitly on 25 July.24 In August a collection of reports suggested that a new Luftwaffe regiment, 155 (W), under Colonel Wachtel, responsible for “radio-controlled bombs,” was to be deployed to France, and that it was also to control batteries of “catapults”; 155 Regiment (W) would later be identified as the flying-bomb operating unit. On 27 August some unclear photographs of the flying bomb which had landed on the Baltic island of Bornholm, but, not identified for what it was, the photos were forwarded to London by the British military attaché in Stockholm. He added that he had heard it was to be fired by “catapult” and that its engine was manufactured by the Argus company in Berlin; both pieces of information bore upon the truth.
In Britain, meanwhile, the high-level quarrel over the “rocket” continued, Lord Cherwell seeking as before to disprove its feasibility. Concern, however, was switching to the reports of the “pilotless aircraft,” and with reason, since, both by British assessment and in reality, it threatened to be the secret weapon that would impact on British territory first. Photographs taken of Peenemünde on 23 June showed four small tailless aircraft on the airfield; these were later identified as prototypes of the Me 163 rocket-propelled fighter (called P30 by the British), but unease continued. On 27 August a report received from the SIS contact in the Waffenamt led all involved to accept that the Germans were developing a flying bomb.25 It remained to discuss its characteristics, the threat it offered and what countermeasures might be effective.
Evidence of the flying bomb’s existence now began to thicken, first from Bletchley. Enigma decrypts of 7 and 14 September were interpreted as references to a pilotless aircraft. It was by then known that two sections of the 14th Company of the Luftwaffe Experimental Signals Regiment, known respectively as Group Wachtel—after the commander of 155 Regiment (W) and Group Insect—were observing test flights at locations near Peenemünde. Their reports, decrypted at Bletchley, clearly referred to a pilotless aircraft, not a rocket, and gave its speed as between 216 and 420 mph, range 120 miles and rate of fall 6,500 feet in 40 seconds.26 Soon afterwards, photographs taken over Peenemünde on 13 November, and a re-examination of others taken in July and September, recorded the presence of a tiny aircraft with a wingspan of twenty feet, propelled by a jet. It was designated P20—to differentiate it from the P30 (the Me 163 rocket fighter, already identified)—and accepted to be the flying bomb so long feared to be under development by the Germans.
The nature of the flying-bomb threat had already begun to gain clarity from other directions. Photographic reconnaissance over northern France, a daily undertaking as the British and Americans accelerated their preparations for the Overlord invasion, started to reveal construction work clearly not connected with coastal defence; reports from agents to SIS and SOE also drew attention to the mysterious structures. By the end of November 1943, 82 sites had been identified, 75 in the departments of Seine-inférieure and Pas de Calais, nine in the Cherbourg peninsula. They took the form of a ramp 150 feet long, curved at one end and aligned on London. Because of their shape, the British designated them “ski sites.”
Sir Stafford Cripps, Minister of Aircraft Production, who took part in the Crossbow meetings, now suggested that they should be bombed on a daily basis. Bombing would be undertaken, but not until a later date. Cripps’ intervention at this stage, in late October to early November, took a less helpful turn, actually diffusing rather than sharpening the focus on essentials. An extremely clever man but a barrister, not a scientist, Cripps attempted in a paper of 2 November to reconcile the differences between the Sandys and the Cherwell schools—between, that is to say, those who believed that the Germans were developing both a rocket and a flying bomb and those who denied the feasibility of a rocket but were prepared to admit the possibility of a flying bomb. Cripps’ dissection of the evidence was meticulous; but, unfortunately, in his conclusions he suggested that it allowed for four, not two, possibilities, in order of priority: (1) a larger HS 293 (the glider bomb mentioned in the Oslo Report and already used by the Germans to sink the Italian battleship Roma); (2) pilotless aircraft; (3) a rocket smaller than the A-4 (V-2); (4) the A-4.
The Cripps report’s conclusions, eccentric as they were, had the effect of drawing attention back to the Sandys point of view, in particular to a memorandum submitted by Sandys to Cripps at the outset of his enquiry. Sandys suggested that the ski sites might not, as was thought by Cripps and others, be potential rocket launching sites but might be connected with the flying bomb. By the end of November the weight of opinion at the Air Ministry (which had assumed responsibility for flying-bomb intelligence) and at the Central Interpretation Unit (where aerial photographs were examined) had moved to that view. It was confirmed on the night of 1 December 1943, when a re-examination of photographs taken recently at Peenemünde disclosed, on a ramp known to have been built in 1942, “a tiny cruciform shape set exactly on the lower end of the inclined rails—a midget aircraft actually in the position for launching.”27
The photograph stilled argument, except from Cherwell. Though it vindicated his long-held view that, if the Germans were developing a pilotless weapon, it would turn out to be a flying bomb—he continued to deny the existence of a rocket—he still quibbled. He denied that it would carry a warhead of more than half a ton, he thought estimates of the number likely to be launched against London were exaggerated, since he doubted that the Germans could produce more than 650 automatic pilots a month (in fact the V-1 guidance system was much more crude) and so on. His was, nevertheless, an increasingly discredited voice. Official Britain now dedicated itself to three anti-flying-bomb measures. First, to establish conclusively what threat it offered. Second, to destroy the ski sites. Third, to organise an active defence, with guns, fighters, balloon barrages and any other device that would bring a V-1 down.
Technical assessment was bedevilled for some months by the belief—held by Cherwell, among others—that the flying bomb, though not an extra-atmospheric rocket, might be rocket-propelled. Then Bletchley decrypts actually perpetuated the confusion because of intercepts from Blizna, the Polish test site, referring to three different fuels, T-stoff, Z-stoff and E1. Only gradually did it become clear that E1 was low-grade petroleum, the fuel on which the V-1 pulse-jet actually worked, while T-stoff (hydrogen peroxide) was used in the launch and Z-stoff (sodium permanganate) was an ingredient of the rocket fuel used by the V-2, which was also test-flown from Blizna. These reports, derived from the breaking of the Luftwaffe key designated Quince at Bletchley, were decrypted during February and March 1944.
Human intelligence provided the next important advance. On 16 April the Naval Intelligence Division at the Admiralty in London received a report from the Stockholm naval attaché of the sighting, on 15 March, by the captain of a Baltic cargo ship, of two flying bombs (described as rocket projectiles) in flight. They had been fired from a shore installation ten miles away and were observed in position 54 degrees 10 minutes north, 13 degrees 46 minutes east (a little east of Peenemünde). They were the size of a small fighter, had short camouflaged wings and were “propelled at a very high speed by a rocket tube which gave approximately 300 detonations a minute” (timed by the captain’s watch). Subsequent questions sent to the naval attaché elicited on 24 April the answers that a cylinder was fixed above the fuselage as a separate unit, that there were no (guidance) wires and that the noise emitted was “a series of explosions, not a continuous rumbling noise.” This marvellously John Buchan observation (Richard Hannay fans would appreciate the captain’s use of his watch) proved eerily accurate: the “detonations” were produced, as would later become obvious, by the automatic opening and closing of the Venetian-blind shutter which admitted air into the pulse-jet tube.28
At the time, though many minds must have worked on the report, the secret-weapons intelligence team failed, rather obtusely, to divine the nature of what the Swedish ship captain had seen. It took further intelligence from Sweden to reveal more. At the end of May 1944, British scientists sent to Sweden were allowed to examine two wrecked flying bombs, one dredged up from the sea bottom by the Swedish navy, another which had crashed on Swedish territory on 13 May. They also received information from the Swedes about two other crashed pilotless aircraft. Their characteristics conformed. Each was a mid-wing monoplane, with a wingspan of sixteen feet, made of steel and designed to be mass-produced, using low-grade petroleum to power an “athodyd.” It was an athodyd to which Mr. Herbert had referred in his preliminary interrogation in 1943, the term describing a pulse-jet. The guidance system consisted of a rudder and two elevators, controlled by three gyroscopes, one of which worked to a compass. “It appeared to have no radio equipment.” The description was accurate. The flying bomb had the crudest of guidance systems. Once launched, it flew at a predicted course and altitude, until the fuel cut-out stopped the engine at a pre-set distance, when it plunged to earth. After 8 June, when this information was passed to the Air Ministry, all important characteristics of the flying bomb were known in London, except, since the stray flying missiles lacked warheads, the weight of explosive it carried. That would soon become apparent. On 13 June the first V-1 landed on London, destroying a railway bridge in the East End. The warhead was calculated to weigh one ton.
That the flying bomb had got through was not for want of effort by the Allied air forces to destroy the launching sites. The ski sites were first deliberately photographed on 3 November 1943, after a French agent reported that the contractor by whom he was employed was building structures, at eight different sites, that he could not identify. Re-examination of earlier photographs and new ones taken after 3 November revealed the existence of ninety-five such structures in northern France, and by late November their resemblance to one of the unexplained structures at Peenemünde had been noted. It was on the Peenemünde structure that the “midget aeroplane,” identified on 1 December, was found by the photographic interpreters. Thereafter it was clear what the ski sites were and that they would have to be destroyed. Neither Air Marshal Harris, of Bomber Command, nor General Spaatz, of the U.S. Eighth Air Force, liked any diversion of effort from their strategic bombing offensive against German cities but higher authority insisted. On Christmas Eve 1943, 672 Flying Fortresses dropped 1,472 tons of bombs on 24 ski sites. The British and American tactical air forces continued the attacks in the spring, but in April, so concerned were the British Chiefs of Staff at the persisting threat that the strategic air forces were employed again. By 12 June 1944, the day before the flying-bomb offensive opened, 23,000 tons of bombs had been dropped, and 8,000 more on what were suspected to be storage depots; in all the tonnage exceeded by half that dropped on London during the German Blitz.29
The bombing proved fruitless. General Erich Heinemann, the German commander of V-1 and V-2 launch units, had always suspected that the ski sites were both too conspicuous and too vulnerable and, after the December attack, decided to abandon them and build at other places, where he laid little more than foundations, the structures to be completed from prefabricated parts at the last moment. He also gave up the large storage structures, making use of natural caves to house his stocks of secret weapons and fuel. As a deception measure, however, some repair work was done at the ski sites, while security was screwed even tighter. The result, for the Germans, was highly satisfactory. Though the sixty-six modified sites were eventually identified, by photographic reconnaissance and from agent reports, intelligence officers failed to persuade their operational superiors that attacks were deserved. It was felt that enough had been done by the bombing of the ski sites, and that the “modified sites” could be attacked if and when a pilotless weapon bombardment started. Only one attack, by fighter bombers, was launched, on 27 May.
The threat, however, had not gone away. On 10 June a Belgian source reported the passage of a hundred “rockets” by rail through Ghent towards the Franco-Belgian frontier; on the 11th new photographic intelligence revealed “much activity” at six of the modified sites, with rails being laid on ramps and buildings completed. On 12 June the British Assistant Chief of the Air Staff (Intelligence) warned the Chiefs of Staff that the Germans were making “energetic preparations to bring the pilotless aircraft sites into operation at an early date.” The next day the first flying bomb fell on London. They would continue to do so until 14 January 1945.
Gun, fighter and balloon defences, deployed to a well-thought-out plan, achieved a measure of success from the outset. On 15 June, 244 flying bombs were launched but by the 21st the guns and balloons were bringing down 8 to 10 a day, fighters 30 a day, and, also because of technical faults, only about 50 a day were reaching London. By July the number had fallen to 25, by August, on one day, 14. The decrease in the number was largely due, however, to the overrunning of the launch sites as the Allied Liberation Armies advanced along the French coast. After 1 September, when Luftwaffe Regiment 155 (W) withdrew to Belgium and then Holland, most flying bombs launched against Britain were dropped from a mother aircraft. On 24 December 1944, fifty aircraft released flying bombs against Manchester, of which thirty crossed the coast and one reached the target.
It nevertheless caused more than a hundred civilian casualties. The V-1 was a highly effective weapon, hated and rightly feared by Londoners and the residents of other British cities it reached. Its approach was signalled by its distinctive pulse-jet beat, the beginning of its descent by silence, its impact by a major explosion. Because of its low terminal speed, it caused destruction over a wide area and heavy loss of life. Deaths inflicted by flying bombs are estimated at 6,184, the severely injured at 17,987. In all, 8,892 flying bombs were launched against Britain from ground ramps and 1,600 from aircraft, of which 2,419 reached the London Civil Defence Region (25 to 30 reached the ports of Southampton and Portsmouth and one Manchester) and another 1,112 landed on English soil; 3,957 were destroyed in flight, by fighters and guns about equally. Balloon barrages intercepted 231. Much of the success of the guns was due to the delivery from America of proximity fuses for their shells, devices which incorporated a miniature radar set, detonating the charge when a target was detected within effective range.30