Operational Use
The first type of aircraft to carry cookies operationally was the Wellington, but they later became part of the standard bomb load of the RAF's heavy night bombers, as well as that of the Mosquitoes of the Light Night Strike Force, whose aircraft would sometimes visit Berlin twice in one night carrying "cookies", flown by two different crews. The 8,000 lb (3,600 kg) bomb, because of its large size, could only be carried by the Handley Page Halifax and Avro Lancaster and the 12,000 lb (5,400 kg) variant only by the Lancaster.
First use of the 8,000 lb was by 15 Squadron Lancasters against Berlin on 2 December 1943. Bad weather and other factors meant their effectiveness was not noted.
The 4,000 lb (1,800 kg) cookie was regarded as a particularly dangerous load to carry. Due to the airflow over the detonating pistols fitted in the nose, it would often explode even if dropped, i.e., jettisoned, in a supposedly "safe" unarmed state. Safety height for dropping the 4,000 lb "cookie" was 5,000 ft; any lower and the dropping aircraft risked being damaged by the explosion.
Read more about this topic: Blockbuster Bomb