By Mark Howell, 100th Air Refueling Wing Historian
/ Published December 30, 2009
RAF MILDENHALL, England -- Project Ruby came about towards the end of World War II due to the failure of the large bombs developed to penetrate the reinforced concrete shielded targets in Germany.
Both the Army Air Force and the Royal Air Force developed a series of heavy bombs to penetrate the heavy protective shielding and included the British 12,000 pound Tall Boy, the 22,000 pound Grand Slam, the American 12,000 T10, and the 22,000 pound T14.
Those powerful explosives failed to penetrate as predicted due to the cases breaking upon impact, the extreme sensitivity of the explosives, or they simply exploded on impact (even before impact) due to the malfunction of the proximity fusing devices.
Another project that ran parallel to the development of large bombs revolved around utilizing rocket assisted bombs to attain high penetrating velocities. The British weapon utilized a 4,500 pound bomb called the Disney.
The bomb could only be carried on the B-17 Bomber due to technical difficulties. The weapon encountered the same problems as Tall Boy and the Grand Slam. Both the RAF and AAF initiated post war testing due to the importance of the asset. As early as June of 1945, the concrete structure at Watten became a target for Trials I, II, and IV. The target proved too small, however, for comprehensive testing, so later, trials took place at Farge, Germany. This reinforced shelter protected the German submarine manufacturing facility during the war.
The structure lay inside the American sector, and thus, the British sought American cooperation to use it as a target. Trial VII completed and Trial IV repeated using the Farge target in August of 1945. In Trial IV, the British 2,000 pound bomb was utilized. Until that point, the American participation only consisted of carrying and dropping the payloads for the British on 40th Combat Wing B-17 aircraft.
Then, because of a rapid retrenchment of organizations, and the elimination of bases in the United Kingdom, United States Air Force European Command issued orders to assign three B-17 aircraft to RAF Mildenhall, England in December of 1945. The RAF Mildenhall site became the base for a joint RAF-AAF operation to bomb the Farge and Helgoland targets.
The program called for the testing of the American 2,000 pound M103, fabricated T-10, and T-14 weapons. The British bombs tested included the Tall Boy, the Disney, and a 1,650 pound model of the 12,000 pound concrete penetrating rocket assisted bomb.
Due to a lack of maintenance personnel, poor supply channels (not to mention weather), and inexperienced personnel, the B-17 aircraft fell short of a successful completion.
Then the AAF sent in a self sustaining team of experienced crews, maintenance, supply, technical, and administrative personnel to expedite the test. The team included three B-29 bombers and four B-17 bombers. This was the official beginning of Project Ruby. The base of operations changed to Marham AB, UK on March 15, 1946.
The bombing operations began on March 25, 1946. The three B-17 aircraft and crews at Mildenhall moved to Marham AB and the testing progressed. The program grew and added the 22,000 pound T-2S (SAP) bomb called Amazon.
Eight trials faced the crews who bombed Farge and tested for penetration, case strength, reliability of fuses, and insensitivity of the exploder device. Nine trials followed at Helgoland to determine the insensitivity of explosive fillers and the performance of the 2000 pound bomb. The SAP bomb tested with 0.10 second delay fuses.
The submarine assembly plant at Farge made an ideal target for penetration and case strength tests. The dimensions came at 1,400 feet by 318 feet with a thickness that varied from 14 feet 9 inches to 23 feet. The building presented different roof reinforcements that proved ideal for testing; however, the proximity to the nearby town of Farge (one house lay within 500 yards and an electric plant just beyond) made it impractical for high explosive bombs.
For that reason, the sensitivity tests took place at Helgoland Island at the U-Boat shelter in the North Sea. The roof proved 10 feet thick and the dimensions approximately 506 feet by 310 feet.
The conclusions of the tests, on Oct. 31, 1946, revealed that none of the bombs tested proved suitable to use against massive reinforced concrete structures. The 22,000 pound SAP Amazon bomb and the 4,500 pound Disney bomb produced the greatest penetration results, but the case strength failed to survive the secondary impact after penetrating the concrete roof.
The rocket 4,500 pound assist bomb simply proved unreliable. All the explosive fillers proved able to withstand the impact of altitude delivery. The D-9 shackle used also proved reliable for use with the 22,000 pound Grand Slam and 22,000 pound Amazon.
The recommendations of Brig. Gen. Carl A. Brandt, USA, insisted that tests continue with smaller diameter, stronger cases, and more pointed nosed 22,000 pound weapons be done at resistant targets.
He thought increasing strength over weight and thickness provided a better product. He also recommended that improvements be made on the reliability of the rocket assist bombs using the same design specifications with a sharper nose, stronger cases, and a smaller diameter.
He insisted the best explosive filler be utilized for the concrete piercing bombs. The shackles used to secure the 22,000 pound bombs proved effective, but cautioned that the tests took place in a temperate climate. Thus began the search for the bunker buster weapons Americans became so familiar with during the last decade of the 20th century.