During the film, the pilots are briefed on using earthquake bombs, however the footage of the bombs arriving at the airfield clearly show the Mark I 1,800 kg (4,000 lb) Blockbuster bomb. The delivery method, construction and effect of the two types of bomb are almost totally opposite. The Earthquake bomb must be released from high altitude for it to attain the necessary speed, and must have a heavy case to penetrate the ground. In the blockbuster bomb, the case is extremely light in comparison to allow maximum explosive payload to flatten buildings at or above ground level.