Mark 5 nuclear bomb

The Mark 5 design was the first production American nuclear weapon which, with a diameter of 39 in (990 mm), was significantly smaller than the 60 in (1,520 mm) diameter implosion system of the 1945 Fat Man nuclear bomb design.

The Mark 5 design used a 92-point implosion system and a composite uranium/plutonium fissile material core or pit.

As with many early US nuclear weapon designs, the fissile material or pit could be kept separately from the bomb and assembled into it during flight.

The Mark 5 had an automatic IFI mechanism which could insert the pit into the center of the explosive assembly from a storage position in the bomb nose.

Approximately 72 Mark 5 weapons were supplied for delivery by Royal Air Force bombers but under US control, under the auspices of Project E.[2] A Mark 5 was used as the primary fission trigger used in Ivy Mike,[3]: 66  the first thermonuclear device in history.

Mark 5 nuclear bomb, side view.
The Mark 5 bomb displaying open doors at front are for insertion of nuclear core
View looking into the nose of a Mark 5, where the fissile pit and final explosive charge segment would be inserted.