Mark 4 (nuclear weapon)/Definition

Still first-generation but a production-quality, re-engineered version of the Fat Man bomb, the yield of which could be varied from 1, 3.5, 8, 14, 21, 22, and 31 kt TNT equivalent by exchanging the plutonium pits; first weapon made on an assembly line rather than by hand; design ancestor of the British Blue Danube bomb