The B46 nuclear bomb (or Mk-46) was a tested but never deployed American high-yield thermonuclear bomb which was designed and tested in the late 1950s. Though originally intended to be a production design, the B46 ended up being only an intermediate prototype which was test fired several times. These prototypes were known as TX-46 units (Test/Experimental). The B46 design roughly weighed 8,120 pounds and was about 37 inches in diameter. It was intended to have a 9 megaton yield.