Atomic Demolition Munitions- Fact versus Fiction
Copyright 2021 by Michael H. Maggelet
One of the interesting aspects of nuclear weapons development was the pursuit of small diameter man portable atomic demolition munitions. Several ADM's were fielded by the US at overseas locations in case of overrun by the Warsaw Pact or communist forces, to be issued to ADM teams to destroy tactical objectives prior to the arrival of invading enemy forces. Some special operations forces were also trained to use ADM's for missions behind enemy lines.
As technology improved, smaller nuclear weapons were fielded to include the gun type T4 and the implosion Mk 54 Mod 0, 1, and 2 Special Atomic Demolition Munition. The Soviet Union also fielded a number of ADM's, and many rumors surrounding these weapons are still on the web, with claims of missing weapons, or those that may have been pre-positioned in European or US caches by KGB or GRU Spetsnaz teams. A 1987 movie starring Michael Caine and Pierce Brosnan entitled "The Fourth Protocol" dealt with a KGB team emplacing an ADM near a US airbase in the UK.
The earliest US man portable ADM was the T4 gun type, which consisted of four separate components each weighing 40 pounds, based off the Mk 9 shell.  No photograph has been publicly declassified or released of the T4, which would be rather interesting.
US Army ADM squad with T-4 components, and UDT/SEAL with B54 SADM
(Photos Los Alamos Scientific Laboratory, and US Navy)
The next man portable ADM was the Mk 54 Mod 0 SADM, which was fielded in April 1963, with mods 1 and 2 in use until the early 1980's. They were intended to be issued to US Army ADM platoons, Army Rangers, Special Forces, and Navy UDT and SEAL teams. There were some interesting procedures required for safing the SADM, or for its emergency destruction. A declassified film on the SADM from Sandia National Labs is linked below, and covers the SADM in very good detail.
In 1992, KGB archivist Vasili Mitrokhin defected to the West and brought along details of KGB operations, agents, and caches of weapons, radios, and large sums of money buried in the US and Western Europe. It has been suggested that the USSR may have buried several ADM's, however there are some technical aspects as to why such weapons would not be functional after several decades of unattended storage (and the fact that these caches were boobytrapped). There is no evidence of the USSR burying ADM's in NATO countries, nor has any ADM been used in terrorist attacks.
Yield of the US B54 SADM reportedly ranged from ten tons up to 1 kiloton, the Soviet ADM from 800 tons to 2 kilotons (see "Spetsnaz- The Inside Story of the Soviet Special Forces" by Viktor Suvorov).
One limitation of long term emplacement of an ADM is that an implosion weapon similar to the W54 SADM would require some preparation and testing before use (such as a continuity test, inspection of the ADM, and inspection of some components such as an explosive plane wave generator, timers, or radio receiver). A gun type weapon would present more problems, due to uranium spalling of the target and projectile, and age of the initiator. While some Soviet cache discoveries have been made public, some items were in pristine condition (such as the R-394KM radio recovered near Morschenich, Germany in August 2019, about 9 km- six miles- NW of a NATO air base). Some components age and the reliability of the munition after decades in the ground would be questionable. GRU Spetsnaz teams of the Army and Navy trained with atomic demolition munitions, as shown in public statements by Russian veterans.
Map showing location of Soviet cache discovered in 2019, northwest of Norvenich, Germany
As for statements that there are "suitcase nukes" on the loose, any gun type weapon requires periodic replacement of its neutron initiators (some US weapons required replacement every six months). Additionally some have stated that plutonium is used in gun assembled weapons, this is not true since plutonium is unsuitable for gun assembled weapons due to pre-initiation concerns.
While US ADM's have been retired and dismantled, there is some evidence that the Russian Federation may retain some ADM's (and it's not beyond the scientific capabilities of the People's Republic of China or any nuclear weapons state, to include the DPRK). With the advent of precision guided munitions, US ADM's have pretty much been relegated to history.
1. "History of the Mk 54 Weapon" by Sandia Corporation. Declassified from "Secret Restricted Data", February 1968.
2. B54 SADM film overview-
Special Atomic Demolition Munition SADM - YouTube
3. "Warsaw Pact Special Operations Forces (USSR/East Germany) and USAFE Operations (1980's-1990's)" by Michael H. Maggelet, Unclassified briefing, May 2021. Presented to the USAF Special Operations School, Language and Culture Center, Hurlburt Field, Florida.