The Grand Slam bomb was a 22,000 lb monster, built to be about the largest thing the astonishing Avro Lancaster could possibly carry. By design, it would impact at supersonic speed, penetrate 40 feet into the ground, and only then explode, the intention being that the shockwave transmitted through the (incompressible, give or take) ground would cause more considerable structural damage over a larger radius than would simply blowing up a ruddy great bomb.
According to the Wikipedia article, the immensely strong casing was cast as a single piece, with the explosive being poured in hot. It subsequently took a month for the charge to cool and set. Accordingly, only 41 were dropped, on targets like bridges and submarine pens.
One used to be on display as the gate guardian of RAF Scampton, home of 617 Squadron. In the late 1950s initial attempts to move the thing by crane were confounded when it turned out to be heavier than expected.
It was live.