Retrieved 29 August 2013.
It falls to earth downwind of the crater and can produce, with radiation alone, a lethal area much larger than that from blast and fire.
An estimated 30% of immediate fatalities were people who received lethal doses of this direct radiation, but died in the firestorm before their radiation injuries would have become apparent.
In July 1944, almost all research at Los Alamos was redirected to the implosion-type plutonium weapon.
A high-velocity gun was no longer required, and a simpler weapon could be substituted.
Three different plants were used so that no one would have a copy of the complete design.
While damage could be studied later, the energy yield of the untested Little Boy design could be determined only at the moment of detonation, using instruments dropped by parachute from a plane flying in formation with the one that dropped the bomb.
A section of the bomb bay door is visible on the top right.