What is the Purpose of a Permissive Action Link?

Introduction A permissive action link (PAL) is an access control security device for nuclear weapons. Its purpose is to prevent unauthorised arming or detonation of a nuclear weapon. The United States Department of Defence definition is: A device included in or attached to a nuclear weapon system to preclude arming and/or launching until the insertion… Read More


What are Letters of Last Resort?

Introduction The letters of last resort are four identically-worded handwritten letters from the prime minister of the United Kingdom (UK) to the commanding officers of the four British ballistic missile submarines. Refer to Operation Looking Glass, Dead Hand, and the Samson Option. They contain orders on what action to take if an enemy nuclear strike… Read More

What is a Counterforce?

Introduction In nuclear strategy, a counterforce target is one that has a military value, such as a launch silo for intercontinental ballistic missiles, an airbase at which nuclear-armed bombers are stationed, a homeport for ballistic missile submarines, or a command and control installation. The intent of a counterforce strategy (attacking counterforce targets with nuclear weapons)… Read More

What is the Balance of Terror?

Introduction The phrase “balance of terror” is usually, but not invariably, used in reference to the nuclear arms race between the United States and the Soviet Union during the Cold War. Refer to Mutual Assured Destruction. Outline It describes the tenuous peace that existed between the two countries as a result of both governments being… Read More

An Overview of Mutual Assured Destruction

Introduction Mutual assured destruction (MAD) is a doctrine of military strategy and national security policy which posits that a full-scale use of nuclear weapons by an attacker on a nuclear-armed defender with second-strike (see below) capabilities would cause the complete annihilation of both the attacker and the defender. It is based on the theory of… Read More

What is a Cobalt Bomb?

Introduction A cobalt bomb is a type of “salted bomb”: a nuclear weapon designed to produce enhanced amounts of radioactive fallout, intended to contaminate a large area with radioactive material, potentially for the purpose of radiological warfare, mutual assured destruction or as doomsday devices. Brief History The concept of a cobalt bomb was originally described… Read More

What was the Special Atomic Demolition Munition?

Introduction The Special Atomic Demolition Munition (SADM), also known as the XM129 and XM159 Atomic Demolition Charges, and the B54 bomb was a nuclear man-portable atomic demolition munition (ADM) system fielded by the US military from the 1960s to 1980s but never used in combat. Brief History and Design At the time of the weapon’s… Read More