Disney Bomb - Post-war Development

Post-war Development

In June 1945, the Air Council wrote to the Lords of the Admiralty expressing "their appreciation" of the work that had been done on the "rocket bomb". The RAF initiated bombing tests of the Disney in June 1945, using the Watten bunker as a target. The actual bombing was carried by the US 8th Air Force on behalf of the RAF. However, Watten proved too small to be a satisfactory target, and the French objected to continued bombing of their territory in peace-time.

Further testing took place as part of Project Ruby. This was a 1946, joint Anglo-American programme to test a range of concrete penetrating bombs against a wartime German bunker on the small island of Heligoland and the Valentin submarine pens. Bombs tested included the Tallboy and the Grand Slam (both British and US-made versions), the American 22,000-pound (10,000 kg) Amazon and 2,000-pound (910 kg) M103 SAP bombs, and the Disney. The bombs dropped on Valentin were inert, as the objective was not to observe the effects of bomb explosions, but rather to test concrete penetration and the strength of the bomb casings. Also, with the resumption of peace, the safety of civilians living around Valentin had become a consideration.

Heligoland was uninhabited at the time as its small population had been evacuated during the war. It was the site of a U-boat pen with a 10-foot (3.0 m) thick roof. This was used to test bombs loaded with explosive (but with inert detonators) to make sure the explosives used were not shock sensitive and would not prematurely detonate upon impact with the target.

This peace-time testing of the bomb was far more extensive than could be carried out prior to its wartime deployment. A total of 76 Disneys were dropped on Heligoland, loaded with a variety of explosive charges, composed of shellite, RDX, TNT or Picratol. Thirty-four Disneys were dropped on Valentin, 12 with the rockets inactivated and 22 with the rockets firing. A further four had been previously dropped on a bomb range at Orford Ness to test their accuracy, and to make sure none would land outside the safety exclusion zone that was set up around Valentin during the trials.

The penetration performance (14 feet 8 inches (4.47 m) of concrete) of the Disney was found to be satisfactory, with a predicted maximum penetration of 16 feet 8 inches (5.08 m). One of the bombs penetrated both Valentin's concrete roof, and its 3-foot (0.91 m) thick concrete floor, coming to a rest completely buried in the sand under structure's foundations. However, there were problems with the bombs. The reliability of the rocket booster ignition was considered unsatisfactory, with a failure rate of around 37% during the trials. Also, some bombs broke up on impact with the target due to flaws in the steel casing and bombs struck at an angle, increasing the effective thickness of concrete they had to penetrate. Furthermore, it was noted that the warhead of the bomb was comparatively small so a very large bunker complex, such as Valentin, would have required many penetrating hits to be sure of destroying all the contents.

In comparison, the effective concrete penetration of the Tallboy and Grand Slams was similar to the Disney (around 14 feet). However, these bombs only directly penetrated around seven feet of concrete and the remaining thickness was blown in by the detonation of the bomb's enormous explosive charge. The roof of Valentin had been penetrated by two Grand Slams before the war ended. But, as no detonation occurred inside the bunker, post-war examination revealed little damage to the complex aside from the large holes in the roof, installations inside the bunker remained comparatively unscathed. The conclusion of Project Ruby was that none of the bombs tested was completely suitable and the development of a new, concrete–penetrating bomb was recommended. However, the Disney's rocket-assist was viewed as a worthwhile feature that should be incorporated into any new bomb designs, as target penetration increases with strike velocity, but it was found this only increases marginally if a bomb is dropped from higher than 20,000 feet (6,100 m).

On 27 January 2009, the body of an inactive Disney bomb, with its 500-pound (230 kg) explosive charge, was extracted from the roof of Watten bunker (by now a private museum), where it had embedded itself during one of the 1945 test-drops. The bomb was transferred to the ammunition depot at La Geule d'Ours – two kilometres from the centre of Vimy – where recovered chemical ammunition and equipment from the First World War is processed.