<P> By August 1945 , the Allies ' Manhattan Project had produced two types of atomic bomb , and the 509th Composite Group of the United States Army Air Forces ( USAAF ) was equipped with the specialized Silverplate version of the Boeing B - 29 Superfortress that could deliver them from Tinian in the Mariana Islands . Orders for atomic bombs to be used on four Japanese cities were issued on July 25 . On August 6 , one of its B - 29s dropped a Little Boy uranium gun - type bomb on Hiroshima . Three days later , on August 9 , a Fat Man plutonium implosion - type bomb was dropped by another B - 29 on Nagasaki . The bombs immediately devastated their targets . Over the next two to four months , the acute effects of the atomic bombings killed 90,000 -- 146,000 people in Hiroshima and 39,000 -- 80,000 people in Nagasaki ; roughly half of the deaths in each city occurred on the first day . Large numbers of people continued to die from the effects of burns , radiation sickness , and other injuries , compounded by illness and malnutrition , for many months afterward . In both cities , most of the dead were civilians , although Hiroshima had a sizable military garrison . </P>
what was the name of atom bomb dropped by usa on hiroshima
Little Boy