For its time, the plane was remarkably futuristic. The all-metal wings were deep and served as fuel tanks, and were fixed to a fuselage with a rectangular cross-section which had room for five crew, with pilot and co-pilot seated in the cockpit alongside the radio operator, and a navigational officer and engineer at the rear. The four Daimler-Benz DB-601 engines were coupled in pairs through a shared gearbox. Work was under way in 1939 and was supported from the highest levels of the Nazi power structure — but with the outbreak of World War II the 1940 Olympics were cancelled, and the project lost both urgency and direction. By August 1939, work had come to a standstill. Within a year, however, it was plain that the war would be no walkover for Germany, and the Luftwaffe began once again to involve long-distance bombers in their strategy. The Adolphine suddenly had a part in these plans, so work was resumed under conditions of urgency and the first prototype flew in December 1940.
It seemed highly promising and, with the DB-606 engines, the range was predicted to be as much as 12,000 miles (20,000km) for the production aircraft. The engines were in short supply, however. They were being produced as fast as possible, but all were needed for established, successful planes like the Heinkel He-177. The second version was flown in 1941, but Messerschmitt realized that the fuel-carrying wings posed a radical problem: there was no room in the wing structure for weapons. There was a plan for the aircraft to fly over New York, dropping propaganda leaflets, but this public relations scheme was abandoned when Allied bombing destroyed both prototypes. There was a third prototype, fitted with two DB-610 engines and with space for two further crew members. It first flew in early 1943 and in April 1943, the Me-261 V3 flew for 10 hours over 2,790 miles (4,500km), the distance from Europe to America across the Atlantic. It was an unprecedented achievement. Three months later the prototype crash-landed, damaging the undercarriage. The plane was used for several long-distance reconnaissance missions but the need for an aircraft to catch the public attention no longer existed, and the project was finally scrapped in 1944.
The idea of a plane that could cross the Atlantic had remained a continuing preoccupation of the German High Command throughout the war. The Commander-in-Chief of the Luftwaffe, Hermann Göring, often spoke of his wish to have a bomber that could curtail the ‘arrogance of the Americans’. One scheme had been to use the mid-Atlantic Portuguese islands of the Azores as a stop for fuel. The Portuguese dictator António de Oliveira Salazar had allowed the Germans to obtain fuel for their U-boats and Navy vessels from São Miguel in the Azores, but in 1943 he signed leases with the British, allowing them to use the islands as a base from which to patrol the North Atlantic by air.
The other designs were all for high-specification aircraft that could fly across the Atlantic and back without touching down. Those that were hurriedly prepared were the all-new Messerschmitt Me-264, upgraded versions of the existing Focke Wulf Fw-200 known as the Fw-300 and the Ta-400, an improved version of the Junkers Ju-290 (the Ju-390) and the Heinkel He-277. Messerschmitt were quick to produce a prototype of the projected Me-264, though in the event it was the Ju-390 which was chosen to go into production. In early 1944, the second prototype Ju-390 reportedly made a trans-Atlantic flight and came within 12 miles (20km) of the coastline of the United States. Another Ju-390 is also claimed to have flown from Germany to south-west Africa (present-day Namibia) early in 1944. These reports are all post-war, however, and are impossible to substantiate.
Many German aircraft companies investigated the problem of bombing the United States of whom Junkers, Messerschmitt, Heinkel and Focke-Wulf were the principal players. Long-distance aircraft were generally seen as impossible to construct in the time-frame, so the plans involved the capture of facilities on the Azores and the use of these strategic islands as a stopping-off point in the middle of the ocean. Bombers including the Ju-290, He-277 and Me-264 would then be within reach of United States targets with a bomb payload of up to 6.5 tons. Targets were listed in detail, and included American producers of light alloys, aircraft engines and optical equipment. Other targets were Canada and an Allied base in Greenland. It was calculated that attacks on American soil would cause the United States to devote her priorities to defending herself, rather than protecting Britain. In this way, the Germans would have less resistance from the British forces and the occupation of the United Kingdom would be easier to attain. However, these detailed plans failed to bear fruit.
The DM-series of delta-winged planes was a joint project of the Darmstadt and Munich Akafliegs (Akademische Fliegergruppen, academic flight research teams). During planning all limits were set aside and what may seem impossible today was seriously considered, such as the DM-4 with a planned wing area of 753ft2 (70m2) that was calculated to reach speeds of 1,000mph (1,600km/h), well above the speed of sound.
These aircraft were not the only delta-shaped planes envisaged in Germany during the war. Alexander Lippisch, the distinguished Munich-born engineer, proposed to develop a ramjet defence fighter powered by a new and highly efficient form of propulsion unit. Rather than relying on air compressed by a spinning turbine, this new design — the ramjet — used the plane’s forward motion to collect and compress the air. Ramjets could operate at very high efficiency, but — because the plane must already be moving to compress the incoming air — they could not be used to propel the plane from a standing start. The ramjet only took over when the plane was already moving at speed. Lippisch named his design Projekt P-13a.
He persuaded the Darmstadt Akaflieg to build a full-scale flying prototype, which the company designated the Darmstadt D-33. Work was proceeding when the Akaflieg Darmstadt workshop was hit during an Allied bombing raid in September 1944, so the D-33 project was transferred to the Munich Akaflieg where the work was completed. They renamed the D-33 the Akaflieg Darmstadt/Akaflieg München DM-1. It was designed as a single-seat glider made from steel tubing and plywood that was impregnated with Bakelite, at the time a highly innovative process. The glider was discovered by United States soldiers when they arrived on site in May 1945, and the prototype was then inspected by Charles Lindbergh who arranged for it to be shipped back to the United States. The prototype was wind-tunnel tested and examined by scientists from the National Advisory Committee for Aeronautics (which later gave rise to today’s NASA — National Air and Space Administration). Among the planes inspired by this German design, as by the Hortens’ flying wing, were the Convair XP-92, America’s first delta-wing fighter, and Convair’s F-102 Delta Dagger which flew in Vietnam. Of a similar, uncompromising delta design was the Convair F-2Y Sea Dart which was a seaplane fighter that took off on buoyant skis from the surface of a body of water.
In Britain, research into the delta-wing concept gave rise to the Handley Page HP-115 and the Fairey Delta 2 or FD2 — the first plane to fly faster than 1,000mph (1,609km/h) — and then the great Avro Vulcan bomber. These are the planes that gave much of the technical data needed in the development of Concorde, the successful supersonic passenger aircraft. Once, when flying aboard Concorde to New York, I was told by a captain that it was not useful to think of Concorde as a supersonic airliner. That didn’t make sense to him — his advice was to envisage it instead as a huge supersonic jet fighter that carried passengers instead of weapons. He was right: that made far more sense.