In order to comply with arms reduction against the START II treaty, the U.S. Navy modified 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.