The bombs then called "Blockbusters" were the RAF's HC (high capacity) bombs. These bombs had especially thin casings that allowed them to contain approximately three-quarters of their weight in explosive, with a 4000 lb bomb (nominal weight) containing about of explosive (Amatol, RDX or Torpex). Most general-purpose bombs, termed "medium capacity'" (MC) by the RAF, contained 50% explosive by weight, the rest being made up of the fragmentation casing. Larger Blockbusters were made later in the war, from the original version, up to .