504th Bombardment Group The 504th Bombardment Group ( 504th BG ) was a World War II United States Army Air Forces combat organization . It was inactivated on 15 June 1946 . The unit served primarily in the Pacific Ocean theater of World War II as part of Twentieth Air Force . The 504th Bomb Group ' s aircraft engaged in B - 29 Superfortress bombardment operations against Japan . Its aircraft were identified by a " E " inside a Circle painted on the tail . The 504th Bombardment Group flew the last combat mission by the United States Army Air Forces of World War II , its last combat mission being on 15 August 1945 . History . The unit was established in early 1944 at Dalhart Army Air Field , Texas , being formed as a B - 29 Superfortress Very Heavy bombardment Group . Thu unit was initially formed with four bomb squadrons ( 393d , 398th , 421st , and 507th ) , being a mixture of both newly - constituted and reassigned units . The 398th was formerly a III Bomber Command B - 25 Mitchell medium bomber Operational Training Unit in the southeastern United states , being formed in 1942 . It later became a B - 26 Marauder Replacement Training Unit until being inactivated in October 1943 . Due to a shortage of B - 29s , the group was initially equipped with former II Bomber Command B - 17 Flying Fortress es previously used for training heavy bomber replacement personnel . The unit was then reassigned for advanced training and received B - 29s at Fairmont Army Airfield , Nebraska during the late spring and summer of 1944 . In May shortages in aircraft and equipment led to the 507th Bomb Squadron being inactivated , with its personnel being consolidated into other group squadrons ( the 507th would be reactivated a month later as part of the 333d Bombardment Group ) . In November , the 393d Bombardment Squadron was reassigned to the to 509th Composite Group at Wendover Field , Utah , leaving the 504th to be a two squadron group . The 393d became the 509th ' s only operational B - 29 squadron . The 393d would eventually become the only military unit in history to engage in Nuclear warfare , dropping Atomic Bomb s on Hiroshima and Nagasaki , Japan , in August 1945 . As a two squadron group , the 504th was deployed to Pacific Theater of Operations ( PTO ) in late 1944 , being assigned to the XXI Bomber Command 313th Bombardment Wing in the Northern Mariana Islands ; being stationed at North Field , Tinian . The group began combat operations from Tinian in January 1945 with attacks on Japanese airfields and other installations on Maug and Iwo Jima and in the Truk Islands . Flew its first mission against the Japanese home islands early in February 1945 when the group bombed the industrial area of Kobe . Continued to attack strategic targets in Japan , operating in daylight and at high altitude to bomb such objectives as aircraft factories , chemical plants , harbors , and arsenals . Switched to night incendiary raids attacking major Japanese cities in the spring of 1945 , causing massive destruction of urbanized areas . Received a Distinguished Unit Citation ( DUC ) for striking the industrial center at Yokohama late in May 1945 . Began incendiary raids in March 1945 , flying at night and at low altitude to strike area targets in Japan . Started mining operations against enemy shipping late in Mar , receiving a 2d DUC for mining Korean shipping lanes , the Shimonoseki Strait , and harbors of the Inland Sea , July – August 1945 . In April and May 1945 the group hit airfields from which the Japanese launched kamikaze planes against the invasion force during the assault on Okinawa . During mid June 1945 the 680th Bomb Squadron was attached to the 504th bomb group to bring the group up to full strength with 3 squadrons . The group continued strategic bombing raids and incendiary attacks until the Japanese Capitulation in August 1945 . After V - J Day , the 504th dropped supplies to Allied prisoners , participated in show - of - force missions , and flew over Japan to evaluate bombardment damage . In the fall of 1945 , the group largely demobilized as part of the " Sunset Project " , with some aircraft being sent reclamation on Tinian ; others being returned to the United States for storage at aircraft depots in the southwest . By Christmas , the group fleet was reduced to 30 or less planes Many of the remaining veterans signed for " any conditions of travel " to get home , arriving three weeks later in Oakland , California , where troop trains scattered them for points of discharge close to their homes . The unit was largely a paper organization when it was reassigned to Clark Field in the Philippines in March 1946 , and assigned to Thirteenth Air Force . At Clark its remaining aircraft and personnel were consolidated into other units , and it was inactivated in June .