thumb|200px|Mark 39 Mod 2 thermonuclear weapon, as found by the explosive ordnance disposal team after the [[1961 Goldsboro B-52 crash|Goldsboro accident in 1961.]]
Laydown delivery is a mode of delivery found in some nuclear gravity bombs: the bomb's descent to the target is slowed by parachute so that it lands on the ground without detonating. The bomb then detonates by timer some time later. Laydown delivery requires the weapon to be reinforced so that it can survive the force of impact.
Laydown modes are used to make weapon delivery survivable by aircraft flying at low level. Low-altitude delivery helps hide the aircraft from surface-to-air missiles.
United States
- B28 bomb — Only in the RE (retarded external), RI (retarded internal) and FI (full-fuzing internal) versions of the weapon. The RE and RI versions of the weapon used the W28 mod 1 warhead and were an interim weapon only capable of laydown delivery at altitude, while the FI version using W28 Mod 2 and later warheads was capable of delivery.
- B43 bomb — Both variants had laydown capability.
- B53 bomb — Full-fuzing option (FUFO) weapon with laydown. The weapon later lost FUFO in its B53-1 upgrade in 1988, having only laydown fuzing.
- B61 bomb — Full-fuzing option (FUFO) weapon with laydown. Capable of laydown delivery at altitude.
- B83 bomb — Full-fuzing option (FUFO) weapon with laydown.
See also
- Air burst
- Toss bombing
- Nuclear bunker buster