The Trident 2 missile (carried by the Navy's missile submarines) carries a mix of W88 warheads (designed for ground burst to destroy hard targets) and W100 warheads (designed for air burst to destroy cities, military bases, or industrial areas). The W100 has a lower yield and is lighter than the W88. When the last arms control treaties reduced the number of deployed warheads, the Navy changed the warhead mix, carrying fewer total warheads although more of them are the heavier W88s. The Navy has now developed a lighter weight radar altimeter and will fit this to the W100 warheads by 2004. This will allow them to be detonated closer to the surface, making them useful for some but not all harder targets.--Stephen V Cole