Three B-29A bombers (serial numbers 45-21747, 45-21750, 45-21751) had touched down at RAF Marham in March 1946 to participate in Project Ruby. That was a joint Anglo-American project to investigate the use of penetration bombs against heavily-protected concrete targets. Initially, The trials took place on a submarine pen on the island of Helgoland. The B-29s mainly bombed the Valentin bunker at Bremer Vulkan on the Weser River with the 22,000-pound Amazon T-2S Semi-Armor-Piercing bomb (the American version of the British Grand Slam bomb). During 1943/44, the vast U-boat bunker Valentin was constructed near the village of Farge. It was supposed to be a heavily protected yard to build submarines using forced laborers from the large concentration camp Neuengamme near Hamburg. The bunker was completed in 1944, but the intended fast U-boat Type-11 production never materialized. In 1946 it provided an excellent test target for the tests of heavy bombs. The bunker was hit eight times with the heaviest conventual bombs, but not with much success. Later that year, three modified B-29s participated in Project Harken, dropping 25,000-pound (11,340 kg) conventional test bombs from 17.000 feet on the Valentin bunker. The B-29s were from the 97th Bombardment Group and stationed at Giebelstadt Air Base, Germany, from 14 July – 4 November 1947.
The former submarine bunker is currently the second largest above-ground bunker in Europe – the largest is the German U-boat pens in Saint Nazaire, France.
The photo shows B-29A 42-63577 releasing a 12,000 lb Tallboy earthquake bomb. From March to June 1945, the USAF was testing the operational suitability of the B-29 for carrying and releasing 12,000-pound Tallboy bombs at the U.S. Army Proving Ground, Eglin Army Air Field, Florida. Photo: U.S. Army Air Force.
Abstract from ON THE EDGE – Part One