Short History of U.S. Earth Penetrator Weapons
The U.S. military has maintained a longstanding interest in EPW’s. In the 1950’s, it
fielded two EPWs, the Mark 8 and Mark 11 bombs. The uranium gun-type Mark 8 bomb
(nicknamed “Elsie” for LC or Light Case) was almost ten feet long, 14 inches in
diameter, weighed some 3,250 lbs, and had a yield of approximately 25 kilotons. In
service from 1952 to 1957, the Navy developed the Mark 8 for targeting underground
facilities, enemy submarines located in sheltered pens, and armored ship decks. The Mark
11 was an improved version of the Mark 8, slightly heavier, and, according to the
National Atomic Museum, “able to penetrate up to 22 feet of reinforced concrete, 90 feet
of hard sand, 120 feet of clay, or five inches of armor plate,” and fuzed to detonate 90-
120 seconds after penetration.
In the 1970s, the Army developed an earth-penetrating W86 alternative to the W85 Pershing
II warhead. In one test a Pershing 1A was launched from Fort Wingate, NM and the earth
penetrator unit impacted at White Sands Missile Range. The penetrator contained warhead
electrical system components, a depth of burial fuzing component, and a telemetry package, but
not the actual nuclear explosive package. It traveled a total of 57 meters through soil on a
diagonal trajectory coming to rest 33 meters beneath the surface. The W86 was cancelled in
September 1980. But during the 1980s, further penetrator tests were carried out to measure
stress and strain. These were done in Nevada and Alaska. At the Tonopah Test Range in Nevada
a 10-meter long recoilless rifle called the Davis gun, was used to fire a penetrator into soft rock.
In Alaska, EPWs were dropped from helicopters onto frozen tundra, near Deadhorse, on frozen
soil at Eielson Air base, and on a frozen boulder field at Fort Greeley. A penetrator dropped from
about 3,000 meters achieves velocities approaching 300 m/s.
In the period from 1986 to 1992, the Department of Energy’s Defense Programs
Office, (now a quasi-independent agency called the National Nuclear Security
Administration, NNSA) conducted underground nuclear explosive tests of “candidate”
warheads for a “ruggedized,” high G-force tolerant “Strategic Earth Penetrator,” and
another weapon, based on the design of the B61-7 strategic bomb, was designated as an
“Interim Earth Penetrator.” The latter program, intended to produce a warhead for a
“shallow” penetrator dropped from aircraft, was completed and entered production in the
mid-1990’s as the B61-11 gravity bomb.