When taking off the Grand Slam aircraft had barely made 1000 feet by the english coast. On They were not supposed to bomb below 14,000 feet because they would be hit by the blast, but one account I read says they bombed at 11,800 feet because that is all the height they could acheive, On releasing the bomb the aircraft jumped up 600 feet.
The Aircrews called the B1 (special) "Clapper Birds", because once the bomb was away, the Lanc was so light and with Merlin 24's they sped home at a speed unobtainable by any other four engined bomber...