text: In May 1946, Operation Front Line began with the participation of US B-29 bombers. Tallboy and Grand Slams were dropped on the  pens and Heligoland; only two hits were achieved from thirteen bombings. The RAF and USAAF reports concluded that none of the bombs were effective against reinforced concrete and suggested more tests in 1947. The tests were resumed after 15 Squadron had finished dropping fifteen bombs on a battleship for the RN. The squadron was down to six Lancasters, four being B.Mk 1 (Special)s, not capable of carrying the  bombs being tested. The other two could carry the bomb but 15 Squadron was re-equipping with Avro Lincolns and six of these were to be altered to carry SABS and radar altimeters. Three USAF B-29s participated again to drop the  bombs from  which was above the ceiling of the SABS.
  The B-29s were also to drop the new US Amazon II and Samson bombs, both , in Operation Ruby II, later called the Harker Project. Photographs taken by 542 Squadron, a photographic reconnaissance unit, before the Grand Slam attack during the war were used to stake out the target with red flags and cameras were set up to film the drops. On 4 August the B-29s achieved six  bomb hits from  and five Amazon II hits out of fifteen from . From 20 September, 15 Squadron Lincolns dropped the  bomb and achieved seven hits, some of which broke on the roof. Tests with a  obtained three hits out of seven.
  Examples
  Five Grand Slam bombs are preserved and displayed in Britain at the RAF Museum, London, Brooklands Museum, RAF Lossiemouth, Dumfries and Galloway Aviation Museum and the Battle of Britain Memorial Flight Visitors' Centre at RAF Coningsby. Casings, without their tails, can be seen at the Kelham Island Museum in Sheffield and Yorkshire Air Museum at Elvington. The T-12 Cloudmaker is an American-made variant of the Grand Slam and an example is displayed at the Air Force Armament Museum in the United States.