The US$503 million program would have converted existing Trident II missiles (presumably two missiles per submarine) into conventional weapons, by fitting them with modified Mk4 reentry vehicles equipped with GPS for navigation update and a reentry guidance and control (trajectory correction) segment to perform 10 m class impact accuracy. No explosive is said to be used since the reentry vehicle's mass and hypersonic impact velocity provide sufficient mechanical energy and "effect". The second conventional warhead version is a fragmentation version that would disperse thousands of tungsten rods which could obliterate an area of 3000 square feet. (approximately 280 square meters). It offered the promise of accurate conventional strikes with little warning and flight time.