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Key specs
- Country
United States- Design
- Gun-type fission
- Type
- Aircraft bomb
- Weight
- 4.4 t
- Length
- 3 m
- Diameter
- 710 mm
- In service
- 1945–1950
Overview
The uranium gun-type bomb dropped on Hiroshima on 6 August 1945, the first nuclear weapon used in war. A cordite charge fired one mass of highly enriched uranium into another; of its 64 kg of uranium, less than a kilogram fissioned, releasing about 15 kt.
The design was considered so certain that it was never tested before use. The B-29 Enola Gay released it over Hiroshima, where it burst at about 600 m; an estimated 70,000–80,000 people were killed outright, and about 140,000 had died by the end of 1945. A few more Mk 1 bombs were assembled after the war and retired by 1950.
Effect radii: estimates
Calculated for 15 kt
- Fireball, maximum radius
- ≈ 180 m
- Initial radiation, 500 rem (5 Sv)
- ≈ 1.4 km
- Blast 5 psi: most buildings collapse
- ≈ 1.8 km
- Thermal: third-degree burns
- ≈ 2 km
- Blast 1 psi: windows shatter
- ≈ 5.4 km
Estimated ground ranges for an air burst at the optimum height over flat, open ground, computed from the yield with standard scaling laws. These are not measurements: real effects depend on the height of burst, terrain, buildings and weather.
Formulas from: Glasstone & Dolan, The Effects of Nuclear Weapons (1977), chapter II; Carey Sublette, Nuclear Weapons FAQ, section 5
Tests and use
| Date | Event | Site | Yield |
|---|---|---|---|
| Aug 6, 1945 | HiroshimaCombat use. Released from the B-29 Enola Gay; air burst at about 600 m. | Hiroshima, Japan | 15 kt |
Test footage
Archive films hosted on YouTube. Nothing loads from YouTube until you press play; the player then comes from youtube-nocookie.com.
Sources
- Complete List of All U.S. Nuclear Weapons, Nuclear Weapon Archive (Carey Sublette)
- Little Boy, Wikipedia