It seemed like such a good idea at the time. Nazi Germany needed a strategic heavy bomber capable of carrying six tonnes of bombs to targets 950 miles from its base and flying at 8,000m, too high for enemy fighters to intercept. However, vector bombsights originally developed during the First World War were still in use during the 1930s and accuracy from high altitude could not be guaranteed. Impressed by the precision dive-bombing of the Junkers Ju87 Stukas during the Spanish Civil War, the Luftwaffe concluded that their new heavy bomber should attack targets by diving.

Heinkel were chosen to manufacture this revolutionary warplane, designated the He177 Greif (‘Griffin’). Weighing eight times as much as a Stuka when fully loaded, the He177 required four engines to meet its performance targets, but the propellers created too much drag for dive-bombing, so Heinkel’s chief designer, Siegfried Gunter, devised a radical solution. Two Daimler-Benz DB601 V12 engines were coupled together to drive a single propeller, creating a four-engined aircraft with only two propellers. Ingenious, but flawed. The twin engines shared a central exhaust system, which overheated and ignited any oil or grease that had seeped from the motors. Engine fires were so common that aircrew nicknamed it the Luftwaffenfeuerzeug or ‘airforce lighter’. Employed for the first time in an anti-shipping role in November 1943,  the captain of an Allied merchant ship reported flames coming from the starboard engine of one of the attacking aircraft.

These were not the only shortcomings of the He177. In order to cope with diving at an angle of 60 degrees, the fuselage had to be lengthened and strengthened, significantly increasing weight and affecting both performance and handling.

To cap it all, by the time the He177 entered active service in January 1942, Germany had developed the Lotfe 7 bombsight, which was accurate from heights of 4,000m, rendering dive-bombing unnecessary. By then it was too late to revert to a traditional four-engined layout, which would have solved the engine reliability issues.

On the plus side, He177 aircrew had a fairly good chance of surviving operations. Gliding down from high altitude to 4,500m to release its payload made it tricky for British radar guiding the anti-aircraft guns to predict its course, while on the Eastern Front, most Soviet interceptor fighters operated at too low a level to catch the He177. In total, 1,169 He177s were built, but events overtook the Luftwaffe’s only strategic bomber one last time. By August 1944 Allied air raids had reduced German production of aviation fuel by 90% compared to May, and all He177s were grounded because scarce fuel was desperately needed for defensive fighters.

Perhaps the final word should go to one of Britain’s top test pilots, Eric Brown, who flew an He177 that had been captured in September 1944: ‘Somehow the He177 always conveyed an impression of fragility despite its size.’ It was ‘one of the very few German aircraft of the period that I tested that I did not enjoy flying.’

Dan Sager