Mark 39 (nuclear weapon)/Definition

U.S. thermonuclear weapon, derived from the Mark 39; 700 built between 1957 and 1959, retired between 1962 and 1966; 3 and 4 MT versions; fuzed for airburst, contact and low-level retarded laydown; safety improved but still alleged to have come close to explosion in 1961 after an aircraft accident