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"10. Bomb, GP, 42,000-lb, T-12
Faced with the possibility of fighting a war in Europe without the benefit of bases in England, the USAAF initiated an intercontinental bomber program in April 1941 for the design of aircraft capable of carrying a 10,000lb bomb load 10,000 miles. Two aircraft designs were funded: the Northrop XB-35 Flying Wing and the XB-36 Peacemaker. Neither aircraft design would realize a flying prototype before the end of the war and only the B-36 would be built in quantity. By late 1942 the threat of a Nazi invasion of Britain had passed, but German U-boats were still taking a staggering toll on Allied ship convoys in the North Atlantic.
The safe haven for these U-boats were the immense submarine pens under construction on the West coast of France. With roofs thought to be made of steel reinforced concrete up to 50 feet thick, these pens would have been impenetrable to the heaviest aerial bombs in existence. Even the 12,000 lb Tall Boy bomb developed for the RAF to destroy hardened or deeply buried targets could not penetrate.30
The Nazi benchmark for a bomb proof structure was steel reinforced concrete 23 ft thick. It was calculated that it would take a 27,000 lb bomb striking at a precise angle and at Mach One to punch through such a structure. This benchmark fails to take into account that it is not necessary to completely penetrate a structure to cause damage inside. The shock waves produced by a large explosion can displace the reinforcement bars causing a 'scab' to detach from the face opposite the one impacted.
The Tall Boy bomb could penetrate concrete to almost 10 ft and scab to a depth over 18 ft. If the target roof was only 16 ft thick, then a large scab could be detached from the inside face of the structure crashing down on anything underneath it. The heaviest weapon used during the war was the 22,000 lb Grand Slam bomb which could penetrate concrete to 12 ft and scab to a depth of almost 23 ft. Because the danger of falling scabs would have been greater than that of outright penetration, a mattress of steel beams was added on the underside of many structures to provide additional strength and catch concrete detached from the ceiling.31
Modeled somewhat on the Tallboy and Grand Slam bombs, design work began in 1942 on what would become the enormous T-12 general purpose bomb. Though designed to weigh approximately 42,000 lb, the practicalities of manufacturing drove the weight to 43,600 lb, 41% (17,600 lb) of which was high explosives. The resulting bomb was nearly twice the size and weight of the Grand Slam. The bomb was 200 inches long, 54 inches in diameter and assembled from six sections of steel welded together. At a total length (with tail assembly) of 322 inches, the T-12 was not merely a scaled up Tallboy or Grand Slam. Several improvements were made by the Ordnance Corps. engineers at the U.S. Army's Aberdeen Proving Ground to correct features that had been copied by war time expediency directly from the Tallboy. By the end of the war, the T-12 had emerged as a purely American bomb design. 32
This T-12 casing stands on its nose at the courtyard of the Aberdeen Proving Ground Museum building. Note the short tail cone when compared to the line drawing below that was adapted from official scale drawings. Several different tail fin configurations were tested and the one used in this display might have been designed for delivery by Boeing B-29 where there was limited space in the bomb bay. U.S. Army/Aberdeen Proving Ground.
The long length of this weapon made it impossible to stow completely inside carrier aircraft during the war and created enormous drag and ballistic problems when carried externally. But a long tail provided the stability essential for precision delivery to the target. The original British design called for tail fin assemblies made of aluminum. These were replaced with assemblies made of steel. The assemblies were attached to the base plate of the bomb by 24 bolts. One suggestion by the AAF was to design a collapsible fin assembly. This scheme was rejected on the grounds that it was overly complicated, prone to delay or failure while opening, which in turn would cause range and deflection errors. Precise placement of these earth quake bombs was essential to achieve maximum effect. British fuzes and detonators had been incorporated into the design initially to save time. These fuzes had no in flight arming feature and this problem was one of the first tackled by Ordnance Corps engineers.33
Work to convert the Renton built Boeing B-29A-70-BA, s/n 44-62263 to carry this weapon was undertaken at Boeing, Wichita during the summer of 1945. Flight testing continued through 1946. Modifications required were the removal of the fuselage center section between the bomb bays, making a cutout in the forward and rear bomb bay doors to fit the contours of the bomb, instruments to record dynamic forces on the airframe during release and recording cameras were installed. Testing followed at Muroc AAFB. Six inert casing drops at an altitude of 25,000 ft were made from March 5, 1948.
Once available, a Convair B-36 bomber joined the test program. The B-36, first flown in 1946, had enormous bomb bays that could easily carry two T-12s or an alternate load of one T-12 and two Tall Boys or Two Grand Slams. On January 29, 1949, B-36B-5CF, s/n 44-92043 flew a 2,900 mile round trip from Ft. Worth, TX to the Muroc AAFB bombing range dropping two T-12s from 35,000 ft and 40,000 ft. At least one fully armed T-12 was tested during the program.34
Illustrations of the loading and lift sequence for the 50,000 lb hydraulic bomb lift. USAF via Dave Cross
From early on it was determined that no practical hoist system could be installed inside an aircraft so Boeing developed the USAF Model No. X50J29603 hydraulic bomb lift. Designed as a low-slung trailer-type vehicle, it could be used to lift bombs from ground clearance blocks then transported over short distances for loading into aircraft. Bombs weighing up to 50,000lb and of diameters from 32 to 54 inches could be handled. A maximum towing speed of 20 mph was possible on paved surfaces when loaded, 30 mph unloaded. The trailer was equipped with electric brakes on the rear wheels powered by the tow vehicle. In the event of a breakaway, the trailer brakes lock automatically. A lever located near the rear wheels allowed manual brake operation. Loading was accomplished by backing the trailer down the length of the bomb.
The hydraulic system was electrically powered. A 28-volt receptacle for external power was located at a control pedestal on the left side at the front of the trailer. Six control levers manipulated pitch, leveling jacks, lift cylinders and roll motors while yaw movement was performed manually. Hydraulic leveling jacks at the front stabilized the trailer. Slings run under the bomb casing were connected to four initial lift cylinders that raised the bomb from ground level to a sufficient height to permit the 5,000lb main lift cylinder carriage to be moved underneath. Mounted on four grooved wheels in steel tracks, the main lift cylinder carriage was locked at the front of the trailer while the initial lift cylinders raised the bomb. After the main lift carriage was rolled under the bomb center of gravity, the initial lift cylinders were lowered until the bomb was at rest on the main lift cradle. The main lift cylinder was made of four telescoping sections with a total height range up to 150 inches with a 22,000lb Grand Slam bomb and to structural limits of 85 inches with the T-12. The main lift cylinder could lift a 50,000 lb bomb 85 inches in about 90 seconds. With a multi-axis movable bomb cradle at the end of the lift piston, the bomb could be manipulated four inches side to side, ten inches forwards and backwards, tilt up and down 6 degrees or be rolled 360 degrees. Because of low ground clearance with the B-29, the lift was rolled into a pit and the aircraft backed over it.35
Multi-axis bomb cradle could precisely load a T-12 bomb in the rack. With some modification, the bomb lift for the T-12 was used to transport and load the 64 inch diameter TX-14 Thermonuclear Bomb that weighed upwards of 50,000 lb. Other TN weapons, like the TX-17/24 followed, which weighed approximately 42,000 lb.
Additional development and testing was carried out until the program was terminated on August 11, 1954. Earth penetrating nuclear weapons that weighed a fraction of the T-12 had made large conventional bombs obsolete. The multi-megaton first generation Thermonuclear weapons tested during the Summer of 1954 had been given the green light for production taking the 50,000 lb bomb lifts that had been attached to the T-12 program. The slings, H-frame and shackles already in B-36 bombers that had been developed for the T-12 were readily converted for the new TN weapons.36
The Army Ordnance Department had placed a war time order of 100 but at the time of contract cancellation only 57 casings had been produced. By that time of cancellation, 50 forged steel and seven cast steel bombs had been assembled by the A. O. Smith Corporation. All seven of the cast bombs and a few of the forged bombs were inert loaded to test ballistics and mating with aircraft. Tritonal was loaded into 20 of the forged casings. Several experimental tail assemblies designated T104, T104E1 and T104E2 were tested with the T-12 bomb. At least one bomb with a T104 assembly was recovered from the hardpan at Edwards AFB after a test drop from 25,000 ft at 300 mph TAS for analysis of the angle of entry, depth of penetration and path through the ground. The results of those tests prompted the manufacture of 36 T104E3 fin assemblies from which seven were sent to Edwards AFB for proposed higher altitudes ballistic tests. It is unclear if these tests were ever carried out since at the time of termination a B-36 aircraft had not been available."
"Molon labe".
Leonidas, King of Sparta,
Thermopylae, 480 B.C.
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