The World’s Smallest Tactical Nuke: The W54, A Bomb That Could Fit In A Man-Portable Carry Case

The Special Atomic Demolition Munition (SADM) was a covert nuclear weapons program developed by the United States Navy in the mid-to-late 1960s.

It utilized the W54 nuclear warhead, which was transported in an H-912 container and deployed by Special Operations Forces.

A two-man team was responsible for placing the device at its designated target, setting the timer, and then making a swift escape.

Their extraction was carried out by either a submarine or a high-speed watercraft, providing a quick and discreet departure.

The SADM (B54) demolition charge version of the W54 in its carry bag.

The W54, also known as the Mark 54 or B54, was a tactical nuclear warhead developed in the late 1950s.

It holds the distinction of being the smallest nuclear weapon ever fielded by the United States in terms of both weight and explosive yield.

The compact design incorporated a plutonium-239 implosion device, and its various modifications allowed for yields ranging between 10 and 1,000 tons of TNT (42 to 4,184 gigajoules).

SADM hard carrying case.

This warhead had two primary applications. One variant was integrated into the AIM-26 Falcon air-to-air missile and the Davy Crockett recoilless gun, while the other was specifically designed for use in the Special Atomic Demolition Munition (SADM) system.

Each version came with multiple modifications, designed for different military scenarios.

A U.S. Army Special Forces paratrooper with the Green Light Teams conducts a high-altitude low-opening military freefall jump with a MK54.

Focusing on the man-portable version, development began in June 1960, leading to the production of an interim model known as the Mark 54 Mod 0 (later designated B54-0) in April 1963.

A refined version, the B54 Mod 1, entered production in August 1964. The weapon measured 12 inches (305 mm) in diameter, 18 inches (457 mm) in length, and weighed 58.5 pounds (26.5 kg).

It was equipped with a warhead, a fuzing and firing system featuring a mechanical timer, a ferroelectric firing set, and a sealed housing.

The body was constructed using aluminum forgings and molded fiberglass, with foam-rubber insulation placed between the warhead and its casing.

To facilitate nighttime operations, tritium-phosphor paint was used to illuminate the dials. Moreover, a specialized housing was provided for underwater deployment, complete with external controls.

The W54 nuclear warhead was used in the man-portable M-388 Davy Crockett projectile. The unusually small size of the warhead is apparent.

Production of the B54 Mod 2 commenced in June 1965. While it retained the same dimensions as its predecessors, it featured design improvements and weighed slightly more at 70 pounds (32 kg).

Atomic Demolition Munition (ADM) employment manuals outline the defensive use of these weapons for combat engineering operations.

The documents specify potential targets, including bridges, dams, canals, tunnels, airfields, railroad marshaling yards, ports, industrial plants, and power facilities.

To ensure appropriate deployment, extensive tables were provided to help determine the correct yield for each target.

These calculations took into account factors such as depth of burial, fallout effects, and minimum safe separation distances between personnel and adjacent detonations.

The W54 warhead in its carry bag.

On December 27, 2018, the Green Bay Press-Gazette published an interview with Mark Bentley, a veteran who trained in the Special Atomic Demolition Munition (SADM) program.

He and other trainees were responsible for manually placing and detonating these devices.

According to the report, soldiers involved in the program understood that their missions were effectively suicidal, either because escaping the blast radius in time was unrealistic or because they were required to secure the site until detonation.

However, ADM employment manuals describe a planned retreat procedure for the firing party and their guards. Once the device was emplaced, security relied on both passive and active defense measures.

Passive measures included concealment, camouflage, and decoys, while active measures involved booby traps, obstacles such as concertina wire and landmines, and long-range artillery fire to deter enemy interference.

Moreover, the SADM was equipped with a Field Wire Remote Control System (FWRCS), which allowed operators to send safe/arm and detonation commands via a wired connection, providing safe remote activation of the weapon.

W54 Warhead

When deployed in the Davy Crockett role, the weapon featured two distinct fuzing systems: a radar-based fuze designed for a 40-foot (12-meter) airburst and a capacitance-based fuze for a 2-foot (0.61-meter) airburst.

These settings allowed for high and low airburst detonation modes, optimizing the weapon’s effectiveness in different battlefield conditions. The device contained 26 pounds (12 kilograms) of high explosives.

Special Atomic Demolition Munition (SADM) Backpack Nuke.

There are conflicting reports regarding the explosive yield of different modifications of the W54 warhead.

Some sources estimate that the Mod 0 version had a yield of 250 tons of TNT (1,000 gigajoules), while the Mod 2 was rated between 10 and 20 tons of TNT (42 to 84 gigajoules).

However, declassified warhead development documents indicate that the primary difference between these two variants was the environmental sensing devices, and that the warheads were field convertible, suggesting that their yields were actually the same.

Official records specify a yield of 20 tons of TNT (84 gigajoules) when the warhead was used in the XM388 round for the Davy Crockett system.

The M28 and M29 Davy Crockett Weapon Systems were tactical nuclear recoilless smoothbore guns developed to fire the M388 nuclear projectile, which was equipped with the W54 warhead.

These weapons were deployed by the United States during the Cold War as part of a broader strategy to provide mobile, battlefield-level nuclear capability.

The project was the first assignment given to the United States Army Weapons Command in Rock Island, Illinois.