n implosion-type fission weapon is a more sophisticated fission weapon.

• An implosion-type weapon uses a complex arrangement of explosives to rapidly compress one or more pieces of fissile material into a supercritical mass.
• The first nuclear weapon ever exploded, at the "Trinity" test near Alamogordo, New Mexico on July 16, 1945, was an implosion-type weapon.
• The "Fat Man" bomb dropped on Nagasaki on August 9, 1945, was also an implosion-type weapon, with an explosive yield of about 21 kt.

Implosion-type weapons are much more difficult to design and build than gun-type weapons.

• They require advanced explosive components and sophisticated fusing systems.

Implosion-type weapons typically require much less fissile material than gun-type weapons.

• A well-designed implosion weapon would require only about 8 kg (18 lbs) of highly-enriched uranium or 4 kg (9 lbs) of plutonium.
  
• This means that implosion weapons can be fairly small and light in weight.

• Implosion-type weapons can use plutonium as well as HEU.