For surface ships, submarines and land-based launchers, Harpoon employs a solid propellant booster to provide initial flight velocity. The booster contains a solid composite cast-in-case propellant which produces an average thrust of 12,000 pounds for approximately 2.9 seconds. After the booster separates, a turbojet engine starts automatically and Harpoon descends to alow-level cruise altitude. It is guided to the target at high subsonic speeds by its midcourse guidance systems and terminal active radar.