Fat Man
The"Fat Man" was the second plutonium, nuclear bomb. The first was the "Gadget" detonated at the Trinity site on July 16, 1945. In the nuclear device, a core of sub-critical plutonium is surrounded by several thousand pounds of high-explosive designed in such a way that the explosive force of the HE (High Explosive) is directed inwards thereby crushing the plutonium core into a super-critical state. Dropped on the Japanese city of Nagasaki on August 9, 1945, it was the second nuclear weapon used in a war.

Fat Man on TinianWeight: 10,800 lbs

Length: 10 ft 8 in.; Diameter: 60 in.

Fuel: Highly enriched plutonium 239

Plutonium Fuel: approx. 13.6 lbs; approx. size of a softball

Plutonium core surrounded by 5,300 lbs of high explosives; plutonium core reduced to size of tennis ball

Bomb Initiator: Beryllium - Polonium

All components of Fat Man ferried to Tinian Island aboard B-29's of the 509th Composite Group

Efficiency of weapon: 10 times that of Little Boy

Approx 1.176 Kilograms of plutonium converted to energy

Explosive force: 21,000 tons of TNT equivalent

Use: Dropped on Japanese city of Nagasaki; August 9, 1945

Nuclear Weaponeer: Cdr. Frederick Ashworth

Delivery: B-29 Bockscar piloted by Maj. Charles Sweeney

This is a picture of "the gadget" in the Trinity Test Site in White Sands, New Mexico

This is a picture of "The Fatman that was dropped on Nagasaki, Japan on August 9, 1945

Little Boy
In this gun-type device, the critical mass is achieved when a uranium projectile which is sub-critical is fired through a gun barrel at a uranium target which is also sub-critical. The resulting uranium mass comprised of both projectile and target becomes critical and the chain reaction begins. Dropped on the Japanese city of Hiroshima on August 6, 1945, it was the first nuclear weapon used in a war.

Weight: 9,700 lbs

Length: 10 ft.; Diameter: 28 in.

Fuel: Highly enriched uranium; "Oralloy"

Uranium Fuel: approx. 140 lbs; target - 85 lbs and projectile - 55 lbs

Target case, barrel, uranium projectile, and other main parts ferried to Tinian Island via USS Indianapolis

Uranium target component ferried to Tinian via C-54 aircraft of the 509th Composite Group

Efficiency of weapon: poor

Approx. 1.38% of the uranium fuel actually fissioned

Explosive force: 15,000 tons of TNT equivalent

Use: Dropped on Japanese city of Hiroshima; August 6, 1945

Delivery: B-29 Enola Gay piloted by Col. Paul Tibbets

Atomic Bomb footage: Tinian (1945)

Also read about:

Sub-critical-below a critical threshold, in particular.

(in nuclear physics) containing or involving less than the critical mass.

comprise- consist of; be made up of.