The term 'WARTHOG WEAPON' is a reference to the A-10 Thunderbolt II, an American ground-attack aircraft. The aircraft is nicknamed the Warthog due to its aggressive look and is armed with a 30mm GAU-8/A Avenger Gatling gun, which is commonly referred to as the Warthog Weapon. The four letter solution to this crossword is 'TUSK', which is a reference to the Warthog Weapon's barrel, which resembles a large TUSK.