Though it sounds like the plot of a movie the reality is that select Army engineers, Special Forces, Navy SEALs, and select Marines were once trained to employ backpack nukes.

The scientists of Los Almos Scientific Laboratory created the W54 atomic warhead in the late ‘50s.  It was one of the smallest nuclear warheads ever fielded at under 11″ diameter (270 mm), about 16″ long (400 mm) and a little over 50 pounds (23 kg).  The fuse allowed for one to select a yield from a tenth of a kiloton to a full kiloton.  The W54 was also a pretty dirty bomb.  People out to a quarter-mile away were likely to receive a deadly dose of radiation.

About 400 W54s were built. The Air Force employed some on AIM-26A Falcon AAM and the AGM-45 Walleye ASMs (to take out Russian bombers and subs, respectively). The Army employed them on the M-29 Davy Crockett, a jeep-mounted recoilless cannon tactical nuclear weapon with about a 3 km range.  That left a couple hundred to be used by SOF as the MK54 Special Atomic Demolition Munition or SADM.  The SADM was designed for a time where the US saw tactical nuclear weapons as a cheap and easy way to make up for capability.

The SADM had a combination lock covering its mechanical timer, which was EMP-proof, mounted in a shockproof case that was waterproof to 200 feet, packed onto a padded ruck.  Total weight of the SADM was a little over 160lbs.

Nuclear weapons at the small-unit level might seem pretty alien today, but early in the development of nuclear weapons their effects were underestimated and utility overestimated.  While most know what Mutually Assured Destruction is, many don’t know the nuanced history and development of US nuclear doctrine.  It evolved from one that promised massive retaliation in the event of a Soviet conventional attack to one of a flexible response.

Massive retaliation was exemplified when Secretary of Defense Forrestal wondered to National Security Council members, in reaction to the Soviets putting barrage balloons up during the Berlin Airlift, “if a reduction of Moscow and Leningrad would be a powerful enough impact to stop a war.”  While promising massive retaliation allowed the US to not have to invest in stronger conventional forces, it became apparent over time that a strategic nuclear exchange was not a solution to many contingencies.  This realization, along with a continued early underestimation of the impact of nuclear weapons, resulted in the development described above of “small” nuclear weapons applied to largely conventional targets.

Special teams chosen from Special Forces units, Navy SEALs, select Marines and Army engineers were trained in the employment of the SADM.  The Atomic Demolitions Munitions School was located at the U.S. Army Engineer Center on Ft. Belvoir, Virginia and was three-weeks long.  Army Special Forces teams attended a compressed weeklong course at Ft. Benning.

SADMs were seen at first as simply super-sized explosives.  Counter-mobility doctrine routinely uses explosives to slow the enemy’s advance, and in Europe, with the overwhelming conventional capability of the Warsaw Pact, any and every advantage to slow down communist forces was considered.  Bridges, tunnels and natural chokepoints were valid targets.  Engineers also envisioned “landscaping” on a huge scale with SADMs creating craters impossible for tanks to traverse, and blowing or creating dams to inundate avenues of approach.