Tactical nuclear weapons include gravity bombs, short-range missiles, artillery shells, land mines, depth charges, and torpedoes which are equipped with nuclear warheads. Also in this category are nuclear armed ground-based or shipborne surface-to-air missiles (SAMs) and air-to-air missiles. Small, two-man portable, or truck-portable, tactical weapons (sometimes misleadingly referred to as suitcase nukes), such as the Special Atomic Demolition Munition and the Davy Crockett recoilless rifle (recoilless smoothbore gun), have been developed, but the difficulty of combining sufficient yield with portability could limit their military utility. In wartime, such explosives could be used for demolishing "chokepoints" to enemy offensives, such as at tunnels, narrow mountain passes, and long viaducts.