The Mk/B53 was a high-yield bunker buster

Nuclear bunker buster

Bunker-busting nuclear weapons, also known as earth-penetrating weapons , are a type of nuclear weapon designed to penetrate into soil, rock, or concrete to deliver a nuclear warhead to a target. These weapons would be used to destroy hardened, underground military bunkers buried deep in the ground...

  thermonuclear weapon developed by the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 during the Cold War

Cold War

The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

. Deployed on Strategic Air Command

Strategic Air Command

The Strategic Air Command was both a Major Command of the United States Air Force and a "specified command" of the United States Department of Defense. SAC was the operational establishment in charge of America's land-based strategic bomber aircraft and land-based intercontinental ballistic...

 bombers, the B53, with a yield

Nuclear weapon yield

The explosive yield of a nuclear weapon is the amount of energy discharged when a nuclear weapon is detonated, expressed usually in the equivalent mass of trinitrotoluene , either in kilotons or megatons , but sometimes also in terajoules...

 of 9 MtonTNT, was the most powerful weapon in the U.S. nuclear arsenal after the last B41 nuclear bomb

B41 nuclear bomb

The B41 was a thermonuclear weapon deployed by the United States Strategic Air Command in the early 1960s. It was the most powerful nuclear bomb ever developed by the United States with a theoretical maximum yield of 25 megatons...

s were retired in 1976.

The B53 was the basis of the W-53 warhead carried by the Titan II Missile, which was decommissioned in 1987. Although not in active service for many years before 2010, fifty B53s were retained during that time as part of the "Hedge" portion of the Enduring Stockpile

Enduring Stockpile

The "Enduring Stockpile" is the United States's arsenal of nuclear weapons following the end of the Cold War.During the Cold War the United States produced over 70,000 nuclear weapons. By its end the U.S. stockpile was about 23,000 weapons of 26 different types...

 until its complete dismantling in 2011.