The key threat in modern naval combat is the airborne cruise missile, which can be delivered from surface, subsurface or airborne platforms. With missile speeds ranging up to Mach 4, engagement time may be only seconds and such missiles can be designed to "skim the sea" mere metres above the sea surface. The key to successful defence was argued to be to destroy the launch platform "before" it fires, thus removing a number of missile threats at once. This is not always possible so the anti-aircraft warfare (AAW) resources need to be balanced between the outer and inner air battles. Missile tactics are now mostly fire and forget in the manner of the Harpoon or Exocet or utilize over-the-horizon targeting, such as the Tomahawk or Silkworm. Close-range missile defence in the modern age depends heavily on close-in weapon systems (CIWS) such as the Phalanx or Goalkeeper.