Overlord'S Blog: Disney's Ruby
On the day Brest surrendered in 1944, Barnes Wallis and three RAF officers took a Jeep into the harbour to inspect the damage Wallis' Tallboy bombs had done to the U-boat pens there. Much to their surprise they'd gotten the time of the cities capitulation wrong, and so were the first allied forces into the port area. The harbour commander offered his surrender to them, which they accepted.
The harbour commander then gave them a tour of the the U-boat pens, he stated to Wallis that the bombs used to penetrate the massive concrete roof were rocket powered. The Tallboys dropped on Brest were not. But later in the war rocket powered bombs would appear. Today I'm going to take a look at them.
Walt Disney produced several cartoons during the Second World War, many were short propaganda cartoons. However in 1942 Walt Disney read the book Victory Through Air Power, and decided that the message contained within the book needed to be made into a popular idea. So Walt Disney produced a film by the same name. The film can be found on Youtube: Here.
It should be noted that by the point in the war the film came out that the Allies were already starting to implement the basic principles of the book. Such as the air campaign against German industry.
The story of the rocket assisted bomb starts with the film. Although there is no proof to say this is how it happened, it is rumoured that a group of Royal Navy engineers from the Directorate of Miscellaneous Weapons Development saw the film in 1943 and one scene caught their interest. The scene shows a rocket powered bomb smashing though the concrete roof of a U-boat pen.
At the time the battle of the Atlantic was in full swing, and the idea of such a weapon, able to hit U-boats while in dock was certainly appealing to the Royal Navy. With support from the admiralty one of the engineers, Captain Terrell started work. The design he eventually came up with was called the Disney Bomb. Its warhead was 500 Lbs of explosive in a massivley re-enforced pointed case. To give you some idea of how heavyilly armoured this bomb was, the total weight was 4500 Lbs.
The rocket power was from 19 rocket motors taken from RP-3 rockets. RP-3's are the iconic weapons seen fitted to the bottom of RAF planes such as the Typhoon.
When dropped from 20,000 feet a mechanical time fuse would be activated. After 15,000 feet the fuse would fire all 19 rockets for a 3 second burn. Accelerating the Disney bomb to 1450 fps (or about Mach 1.29). The impact would smash the bomb through 13 feet, 10 inches of reinforced concrete before the warhead detonated. In one post war test a Disney over-penetrated the roof and the floor of the target and buried itself in the ground below.
Without suitable targets to test the bomb on it was decided to put the bomb into service based solely on the mathematical calculations. As it turned out those calculations were exactly right. Some test drops were carried out to enable bomb sights to be calibrated. Due to technical issues, that I've not yet been able to find out about, the only plane that could carry the Disney bomb was the B-17. A pair of bombs would be slung under the fuselage of each plane.
On the 10th of February, 1945, the 407th Bomber squadron joined up with its parent unit, the 92nd Bomber group, and headed for Ijmuiden the E-boat pens.
At Ijmuiden there were two E-boat pens that sheltered the fast attack craft that raided cross channel shipping at night.
Of the entire 92nd group's 164 planes only 9 carried Disney bombs. The group lined up on the second much larger bunker and bombed together. The bunker was hit and penetrated successfully. However the E-boats weren't there. The bunker hadn't been completed yet. Four days later the 92nd repeated the bombing, this time aimed at the first smaller bunker. Due to its smaller target size the aircraft bombed on their own, and not as was the usual practice all at the same time. The effects of the bombing are not recorded.
On 30th of March the 92nd and 303rd Bomb groups joined together to attack Bremen. Heavy flak caused major damage to 13 aircraft and wounded 4 airmen of the 303rd. As the formation approached the target the lead plane took damage from Flak to its wing and lost both engines, after slipping out of the formation it was lost to sight. Eventually it crash landed in a corn field and all the crew were captured unharmed. The only other incident was when a lone ME262 made a single attack run on the formation, failing to cause any significant damage.
The target for the Disney's was the Valentin U-boat factory. Only one Disney hit the target causing minor damage. However the massive number of normal bombs dropped on the area from the two bomb groups caused such damage to the surrounding facilities that the site was abandoned by the Germans.
The final target for the Disney bomb was Hamburg submarine pens on the 4th of April. Due to cloud cover the bombers tried to bomb using radar, however no Disney's scored any hits. Again the supporting bombers did damage, sinking three U-boats. The 92nd lost a single plane in this raid. Rapidly running out of targets for Disney's and with the war drawing to a close there were no more Disney missions.
Although the story doesn't quite end there. After the war tests were carried out, under the name of Project Ruby. These included most of the bombs used for concrete penetration, such as the Tallboy, Grand Slam and Disney bombs. At first the targets were in France, until the French objected to still being bombed despite the war being over. So a selection of targets in Germany were used. The tests showed that the Disney had roughly the same performance as the Tallboy bombs. Also that a portion of penetration from both bombs came from the warhead exploding after the bomb had seated itself. Two flaws in the Disney's design were discovered. First the rocket motors had reliability problems, and second the bomb wasn't very accurate.
The final entry in the Disney's story comes from 2009 when the French discovered one of the Disney's that had been used in the early tests, still with its warhead intact. The bomb has since been recovered and stored by the French military.