the four oldest Ohio-class Trident submarines (, , , and ) to SSGN (Ship, Submersible, Guided, Nuclear) configuration. The conversion was achieved by installing vertical launching systems (VLS) in a configuration dubbed "multiple all-up-round canister (MAC)." This system was installed in 22 of the 24 missile tubes, replacing one large nuclear strategic ballistic missile with 7 smaller Tomahawk cruise missiles. The 2 remaining tubes were converted to lockout chambers (LOC) to be used by special forces personnel who can be carried on board. This gives each converted sub the capability to carry up to 154 Tomahawk missiles. The MAC tubes can also be used to carry and launch UAVs or UUVs which give the ship remote controlled "eyes & ears" allowing the ship to act as a forward-deployed command & control center. The "boomers" were named for patriots, and together with the , , , and es, these SSBNs comprised the Cold War-era "41 for Freedom." Later Ohio-class submarines were named for states (recognizing the increase in striking power and importance once bestowed upon battleships), with the exception of , which was named for United States Senator Henry M. "Scoop" Jackson (1912–1983) of Washington upon his death while in office (1983). This honor was in recognition of his advocacy on behalf of the nuclear submarine program. He strongly supported the rapid development of nuclear submarines and especially the development of an SSBN program. Senator Jackson also called for the establishment of a Deputy Chief of Naval Operations for Undersea Warfare because he believed submarines were "lost in a welter of naval bureaucracy." Personnel U.S. Navy submarines are manned solely by volunteers from within the Navy. Because of the stressful environment aboard submarines, personnel are accepted only after rigorous testing and observation, as a consequence submariners have significantly lower mental hospitalization rates than surface ship personnel. Furthermore, submariners receive submarine duty incentive pay (SUBPAY) in addition to sea pay. Some 5,000 officers and 55,000 enlisted sailors make up the submarine force. In addition to submarines, they are assigned to submarine tenders, submarine rescue ships, deep-diving submersibles, floating dry docks, shore support facilities, submarine staffs, and senior command staffs. Until 2014, submarine watchkeeping had an 18-hour day, as opposed to a standard 24-hour schedule. Sailors spent 6 hours on watch, 6 hours maintenance and training and 6 hours off (3 watches of 6 hours.) In 2014, the Navy began transitioning the fleet