The U.S. Navy is spending some $200 million to upgrade and test the
Mk 6 guidance systems in its 425 Trident II D5 SLBMs (sea launched ballistic
missiles). The missiles are carried by American SSBNs (nuclear powered
ballistic missile submarines.) The guidance systems are 1980s technology, and
some of them are twenty years old as well (production of the Trident II D5
ended last year, although another hundred or so missiles may still be
produced.) The upgraded guidance systems will be more accurate, reliable and
easier to maintain.