Mark 4 nuclear bomb



The Mark 4 nuclear bomb was an American nuclear bomb design produced starting in 1949 and in use until 1953.

The Mark 4 was based on the earlier Mark 3 Fat Man design, used in the Trinity test and the bombing of Nagasaki. The Mark 3 design was essentially handmade and designed as an emergency wartime expedient design; the Mark 4 utilized essentially the same basic design (materials, dimensions of the nuclear core and explosive components) but reengineered the whole design to be safer and easier to produce. The basic ideal was to "GI-proof" otherwise sensitive nuclear weapons.

The Mark 4 was 60 in in diameter and 128 in long, the same basic dimensions as Mark 3. It weighed slightly more at 10800 to 10900 lb depending on the specific Mark 4 version (Mark 3 weighed 10200 lb).

In addition to being easier to manufacture, the Mark 4 introduced the concept of in flight insertion or IFI, a weapons safety concept which was used for a number of years. An IFI bomb has either manual or mechanical assembly which keeps the nuclear core stored outside the bomb until close to the point that it may be dropped. To arm the bomb, the fissile nuclear materials are inserted into the bomb core through a removable segment of the explosive lens assembly, which is then replaced and the weapon closed and armed.

Mark 4 models used composite uranium and plutonium fissile pits. The exact pit assemblies were common with several other US nuclear weapons, the Type C and Type D pit assemblies.

Various versions of the Mark 4 had explosive yields of 1, 3.5, 8, 14, 21, 22, and 31 kilotons (4 to 130 TJ).

A total of 550 Mark 4 nuclear weapons were produced.

The Mark 4 was succeeded by the Mark 6 nuclear bomb, which was generally similar but much improved.

W4 missile warhead
A variant called the W4, intended for use on the Snark missile, was designed but never built. The W4 design was cancelled in 1951.