Four U.S. Navy Ohio-class SSBNs were converted in the mid-2000s to be able to salvo launch up to 144 Tomahawk cruise missiles from their modified vertical launch SLBM tubes, as opposed to launching cruise missiles from torpedo tubes as is done from attack submarines. The advantage that the submarines have over guided missile destroyers and cruisers is the ability to remain undetected and launch while submerged. Tomahawk was deployed on US Navy attack submarines beginning in 1983, originally in LACM and ASCM versions, but the ASCM version was withdrawn in the 1990s.