An Intercontinental Ballistic Missile, or ICBM, is a long-range (greater than 5,500 km or 3,500 miles) ballistic missile typically designed for nuclear weapons delivery, that is, delivering one or more nuclear warheads. Due to their great range and firepower, in an all-out nuclear war, submarine and land-based ICBMs would carry most of the destructive force, with nuclear-armed bombers the remainder. ICBMs are differentiated by having greater range and speed than other ballistic missiles: intermediate-range ballistic missiles (IRBMs), medium-range ballistic missiles (MRBMs), short-range ballistic missiles (SRBMs) these shorter range ballistic missiles are known collectively as theatre ballistic missiles. Categorizing missiles by range is necessarily subjective and the boundaries are chosen somewhat arbitrarily.