A cruise missile submarine is a submarine that can launch cruise missiles (SLCMs). The United States Navy's hull classification symbols for cruise missile submarines are SSG and SSGN - the SS denotes submarine, the G denotes guided missile, and the N denotes that the submarine is nuclear-powered. Many cruise missile submarines retain the capability to deploy nuclear warheads on their missiles, but they are considered distinct from ballistic missile submarines due to the substantial differences between the two weapon systems characteristics. In modern usage, there is some significant overlap between cruise missile submarines and traditional attack submarines, as both cruise missile and dedicated anti-ship missiles greatly enhance a vessel's ability to attack surface combatants. Torpedoes are a more stealthy option, but missiles give a much longer stand-off range, as well as the ability to engage multiple targets on different headings at the same time. Early cruise missile submarines had to surface to launch their missiles. Later designs launch missiles from underwater, using either torpedo tubes or vertical canisters.