Thursday, April 23, 2015

Bomber Command in Crisis, 1941–42 Part II

There are many explanations for the crisis now confronting Bomber Command. The new strategy of attacks on city areas was only possible with better equipment, and the directives failed to take sufficient account of what technology was currently available. The most pressing need was for larger aircraft capable of carrying a much greater tonnage, dropped with greater accuracy. This was an obvious solution, and the pressure to accelerate output and improve navigation came from all sides. 

Yet the heavy bombers that Churchill had been shown in July were still only available in very small numbers because of persistent problems with technical development, while improved navigation was still at the experimental stage despite more than eighteen months of war. The Stirling and the Halifax made their first sorties in February and March 1941. The Short Stirling Mk I was the only one of Britain’s wartime bombers designed from the start to have four engines. It was first commissioned in 1936, the prototype made its first successful flight in December 1939, and the first aircraft came into service late in 1940. Powered by four Bristol Hercules engines, the Stirling had a top speed of 270 miles per hour and a range of 590 miles with a full bomb load of 14,000 pounds. It had a limited flying ceiling but good defensive capabilities with three powered turrets, yet it was plagued with technical problems that had to be ironed out in 1941 and early 1942. The same was true for the Handley Page Halifax, which also stemmed from a 1936 specification and was originally designed as a twin-engine medium/heavy bomber. In 1937 it was converted to four Rolls-Royce Merlin engines, and the prototype flew in October 1939. The Halifax Mk I was developed rapidly and was in service by November 1940. Its first operation, against the French port of Le Havre, was made in March 1941. 

It had a low operational ceiling of 18,000 feet, a top speed of 265 miles per hour, and a range of 1,260 miles with a maximum bomb load of 13,000 pounds. The aircraft exhibited persistent development problems, had slow handling characteristics, and took high losses. Output continued because it was difficult to disrupt production schedules already laid down, but it was an unpopular aircraft with bomber crews.

The third heavy bomber, the Avro Lancaster, grew out of another twin-engine development, the Manchester, also first specified in 1936. The Manchester was designed around twin Rolls-Royce Vulture engines, but these proved to be a constant source of technical delays. The prototype flew in July 1939, and the first service aircraft were delivered in November 1940. The first raid was against the French port of Brest in February 1941, but repeated engine failure led to the cancellation of further production and only 209 were built. In late 1940 a Manchester Mk III was produced with four Rolls-Royce Merlin engines. It was renamed the Lancaster, and for Bomber Command it was an unexpected godsend. The Lancaster had a much better performance: a top speed of 287 miles per hour, a ceiling of almost 25,000 feet, and a range of over 1,000 miles even with its heaviest load of 22,000 pounds. The usual load was somewhere between 14,000 and 18,000 pounds and the range correspondingly farther. Its carrying capacity was larger than that of any other bomber used in the European theater, and four or five times that of the standard German medium bombers. Some 6,750 Lancasters were produced during the war, the mainstay of the later force. Unlike the Halifax, the Lancaster had a more modest loss rate (3.92 percent compared with 5.75 percent), absorbed less production effort, carried an average of almost twice as much bomb weight, and was easier to service.136 But it only began operations in modest numbers in 1942. In 1941 the small total of heavy bombers dropped only 4,000 tons, against the 31,500 tons dropped by the Wellington medium bombers.

The advent of heavier aircraft would mean that the RAF could take advantage of both a new generation of heavier bombs under development and the rapid expansion of bomb production. The prospect of increasing the aggregate payload was regarded as the critical factor in the offensive, but it had to be postponed until the heavy bomber force became available. The 250- and 500-pound General Purpose bombs were still extensively in use in 1941; larger 1,000-, 2,000-, and 4,000-pound bombs, more suitable for the larger bomber models, were developed during the Blitz and brought into use in small numbers. These Medium Capacity (MC) and High Capacity (HC) bombs had a higher charge-to-weight ratio, a thinner metal shell, and a much greater blast effect. However, they still lacked aluminized explosive, which would have increased that effect more than threefold; only later in the war was Lindemann finally able to persuade the RAF to adopt it. The 4-pound incendiary bomb remained standard equipment but was supplemented by the larger 30-pound firebomb with a blend of phosphorus, rubber, and benzol gel, 400,000 of which were ordered in June 1941 and 3 million used by the end of the war. All these bombs became available in quantities too large for the existing bomber force to use. In April 1941, 12 million incendiaries were ordered for the rest of the year and 36 million for 1942; because of magnesium shortages, however, output was only 2.2 million in the nine months of 1941 and 11.8 million in 1942, but these figures were more than enough for a force not yet converted fully to mass incendiary bombing. By the end of 1941 there was a surplus of more than 2 million bombs, and monthly production was double monthly expenditure. By the summer of 1941 around 11,000 tons of high-explosive bombs were being produced and filled every month, though Bomber Command had dropped an average of just 948 tons a month between January and April and averaged only 1,884 tons on Germany between July and December. In October 1941 there were unused stocks of 121,000 tons of bombs. This was the reverse of the German problem during the Blitz, when there had been the airplanes but insufficient filled bombs; the RAF had the bombs but not enough heavy and medium bombers to use them.

Both the new aircraft and the new bombs were slow to join Bomber Command in any significant numbers. Only 41 heavy bombers were produced in 1940 and 498 in 1941, compared with an output of 4,703 medium bombers. These were modest figures against the plans drawn up in the spring of 1941 to create a force of 4,000 heavy bombers by the spring of 1943. Bomber production had taken a backseat during the summer and autumn of 1940 when priority went to fighter aircraft for defense against German raids. The minister of aircraft production, Lord Beaverbrook, was later blamed by the Air Ministry for trying to kill off “the Big Bomber programme,” but this ignored the serious technical problems encountered in trying to develop and get into service large and complex aircraft in a matter of months. In May 1941, Portal informed Beaverbrook’s successor, John Moore-Brabazon, that he did not want any further heavy bombers developed during the war because of the long lead time between designing a bomber and seeing it into service. The “4,000 Plan” was always unrealistic. It called for production of at least 1,000 bombers a month over a two-year period, more than twice the number produced during 1941 and 1942. It was already evident by the summer of 1941 that bomber production had hit a serious bottleneck. The RAF pinned its hopes on being able to persuade the United States to make up the shortfall.

The efforts to get America to solve Britain’s bomber crisis went back to the early spring of 1941, when Lend-Lease was finally approved. The RAF delegation in Washington had the challenging task of persuading the American service chiefs to accept the transfer of substantial quantities of modern aircraft, and in particular heavy bombers, from their own rearmament program. Air Vice Marshal Slessor negotiated the aircraft requirements with the Army Air Corps, commanded by General Henry “Hap” (for “Happy”) Arnold. The American offers were enshrined in what became known as the Slessor-Arnold Agreement, a generous commitment, subject to circumstances, to supply Britain on a 50–50 basis from all American aircraft production. The agreement failed, however, to address the problem of the heavy bomber, where Britain’s deficiency was most marked and American output still in its infancy. Arnold visited Britain in April 1941 and was told that the British aircraft industry could not produce more than 500 of the 1,000 heavy bombers needed each month. The United States was asked to fill the gap. Arnold agreed that up to four-fifths of American heavy bomber output could go to Bomber Command by the summer of 1942, but this would consist of fewer than 800 aircraft. By then it was evident that the American air force would renege on the original agreement as relations with Japan deteriorated. At the staff discussions at the Churchill-Roosevelt Argentia summit at Placentia Bay in August 1941, Arnold refused to confirm the American offer. In his diary he noted, “What the British want—my God what a list and what things—no promises.” During September the full extent of American withdrawal from the initial Slessor Agreement became clear. The bombers destined for Britain had been fitted with the Norden bombsight, which was still embargoed for British use, and ensured that the bombers could not be released to the RAF. Instead of the 800 bombers expected, the British were granted 238 with no promise of any further deliveries beyond July 1942. It marked the end of the Slessor Agreement and the end of any prospect of developing a force of 4,000 bombers.

The most urgent problem facing Bomber Command was the search for some form of electronic aid for navigation, without which even larger numbers of bombers would still have restricted striking power. In the summer of 1941 the problem was not simply the failure to hit a precise industrial or railway target, but the inability, under conditions of night, poor weather, and German defenses, to find an entire city. Given that these failures almost nullified what Bomber Command was trying to do, the long period that elapsed in trying to find appropriate tactics or technology is difficult to explain. The technology itself was not exotic, and the capacity to interfere with German electronic navigation in the winter of 1940–41 made evident that British science was capable of replicating German practice. The Telecommunications Research Establishment had begun work on a system using radio pulse transmitters in 1938, known as G (for Grid), but usually described as Gee. The system worked by sending pulses from three ground stations that could be measured on a cathode-ray tube carried in the receiving aircraft; where the coordinates intersected it was possible to estimate to between a mile and six miles the aircraft’s position. Like the German system, it had limited range and was less accurate the farther away from the ground stations the aircraft was. It worked generally no farther than western Germany. The system was shown to Bomber Command in October 1940, and service trials began in May 1941. The first experimental operation using Gee was conducted by two Wellington bombers on August 11, 1941, but one crashed on German soil. The delay in introducing Gee was partly a result of delays in the production of one of its vacuum tubes, but the main problem was the argument between those who favored putting Gee in a small number of target-finding aircraft, which would lead in the rest of the force, and those who argued that it was something that should be made widely available for the benefit of all. This was to become a central conflict in deciding the best tactics for attacking German cities, and it undermined efforts to develop a more appropriate operational system more rapidly. The use of Gee was postponed until enough sets were available to supply much of the command; its first operational use was not until March 8, 1942.

The arguments over the introduction of Gee also involved the best tactics to adopt to achieve Bomber Command’s new objectives and to counter the threat posed by German antiaircraft defenses. Since the summer of 1940, when the German Air Force had relied principally on antiaircraft fire, a more sophisticated defensive system had been constructed combining antiaircraft fire, night fighters, searchlights, and radar. The original air defense system, like that of the British, had been based on the assumption that attacks would come by day. The German defenders soon realized that the pattern of British bombing was difficult to predict. A few daylight raids were made, but most raids were small night attacks defined because of their modest scale as nuisance raids (Störangriffe), whose object, it was assumed, was to intimidate the population and disturb the rhythm of industrial labor. Then came heavier raids in the spring of 1941, again scattered and unpredictable but deliberately directed, so the German authorities believed, against “open cities and residential areas” as simple terror attacks. Night attacks meant that antiaircraft fire, without radar assistance, was effectively blind. The decentralized pattern of British raiding made it difficult to know what to protect. German air observation posts were set up around fifteen to twenty kilometers from predicted target areas, but nighttime conditions reduced the prospect of accurate information. The numerous sound detectors used in conjunction with searchlights were found to be vulnerable to the British tactic of throttling back the engines to dampen the noise as aircraft approached a potential danger zone. (British crews also believed that throwing empty milk bottles or beer bottles out of their aircraft confused enemy equipment. The “whistling bottle” was said to interfere with sound location and trigger the searchlights to switch off.) For the German side a concerted defense was difficult to mount, because RAF bombers failed to damage essential war-economic targets, which were guarded by “air defense strongpoints,” and instead scattered their loads over an extended area with few evident objectives. The Butt Report could essentially have been written by the Germans months earlier.

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