The W-61 EPW (earth penetrating warhead) project began in 1989. The EPW was a derivative of the B61-7, packaged in a high-strength steel case, and had gotten as far as production engineering in 1991.
The B61-11 is a new Mod of the B61 being converted from existing B61 Mod 7s. The basic differences in the two Mods are in the nose and tail configurations, and the elimination of the B61-7 parachute and gas generator. The similarities are that all B61-11 internal case hardware and components, including the IHE physics package and warhead electrical system, are from the B61-7. Some sources suggest that the B61-11 has a "dial-a-yield" feature, allowing its yield to range from less than a kiloton to several hundred kilotons. When configured to have a 10-kiloton yield and detonated 4 feet underground, the B61-11 can produce a shock wave sufficient to crush a bunker buried beneath 100 meters of layered rock. However, the December 2001 Nuclear Posture Review noted that "This single-yield, non-precision weapon cannot survive penetration into many types of terrain in which hardened underground facilities are located."
Stockpiled since 1968, the veteran B61 has been modified many times over the years to update its performance. Its latest modification is the B61 Mod 11 "earth-penetrater." The United States deployed the B61–11 bomb in the mid-1990s for an earth penetrating mission. The B61-11 is a new Mod of the B61 being converted from existing B61 Mod 7s. The basic differences in the two Mods are in the nose and tail configurations, and the elimination of the B61-7 parachute and gas generator. The similarities are that all B61-11 internal case hardware and components, including the IHE physics package and warhead electrical system, are from the B61-7.
Designed to replace the aging B53 "laydown" weapon, the much smaller and less powerful B61 can produce the same destructive ground shock as the massive B53, but without the collateral damage associated with a surface blast. The B61-11 was designed not to penetrate rock but to attack only certain targets in hard or frozen soil in Russia.
