Despite nuclear disarmament treaties, the U.S. is still building ICBMs. Twelve Trident II (D-5), three stage ballistic missiles, for use by SSBNs, are under construction. The missiles cost $47 million each. The nuclear warheads are extra. The 58.5 ton Trident II equips the 18 Ohio class SSBNs. The missile has a range of 7,400 kilometers and is more accurate than the Trident I it is replacing. The Trident II can deliver up to five warheads. The missile entered service in 1990, while Ohio SSBN boats were still being built (the last one entered service in 1997). Older Trident boats are now having their Trident I missiles replaced with Trident IIs. Each Trident SSBN carries 24 missiles (120 warheads.) The 18 Ohio class SSBNs carry half the United States's nuclear warheads.