509th Composite Group (USAAF)

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The 509th Composite Group (USAAF) was formed specifically to drop the atomic bomb, and carried out the attacks on Hiroshima and Nagasaki that helped end the Second World War.

A great deal of effort went into the formation of the group. Col Paul W. Tibbets, Jr, a combat veteran who was then testing the new B-29 was chosen as group commander during the summer of 1944. Tibbets chose Wendover Field, Utah, as the group's base because its isolation made tight security easier. An existing bombardment squadron, the 393rd, was chosen to carry the bomb, moving to Wendover from Nebraska in September 1944. The bombardment squadron was supported by the 320th Troop Carrier Squadron, the 390th Air Service Group (603rd Air Engineering Squadron and the 1027th Materiel Squadron) and1395th Military Police Company (Aviation), with the aim of making it as independent of outside help as possible.

The group also gained two units directly associated with the bomb - the 1st Technical Detachment, War Department Miscellaneous Group was a mixed group of military and civilian scientists and technicians while the 1st Ordnance Squadron Special (Aviation) had direct responsibility for the bombs themselves.

The training programme was tailored to the group's special mission. Bombing tests with dummy bombs were carried out at Wendover (using special models with an inert filler). In January 1945 the group carried out high altitude and long range over-water training from Batista Field, Cuba, but no formation training. In May specially modified B-29s arrived. These had all but the tail guns removed, and changes made to allow the very large atomic bombs to be carried.

In February 1945 it was decided to base the new group at North Field, Tinian. This required the construction of extra hard standing at this airfield, which was still under construction at the time. The secrecy surrounding the new group's mission had caused some problems during this period as it's mission wasn't originally explained to Nimitz. As a result he initially refused to give priority to its requirements and a naval officer had to be sent out from Washington to explain the group's importance.

The group began to arrive at its new home on Tinian in May 1945 and was fully installed by June. The first ground echelon sailed from Seattle on 6 May. The advanced air echelon overtook it, flying in to Tinian on 18 May, with the ground echelon arriving by sea on 29 May. The B-29s and their crews began to arrive by air on 11 June and the entire group was installed by the end of July.

The group immediately stood out on Tinian. It ignored the normal command structures, answering in practice to the highest levels in the USAAF and eventually to the President. Strict security precautions remained in place and the new group didn't take part in normal bombing operations.

Between 30 June and 22 July the group went through the standard combat training regime for new B-29s groups. This involved a series of raids on bypassed Japanese island garrison, where the high flying B-29s would come under attack, but without risk as they were flying well above the range of Japanese anti-aircraft guns or surviving fighters). Most crews started with a flight to Iwo Jima, bombing Rota on the way back, two shorter missions to bomb Rota or Guguan, one long range attack on Truk and another against Marcus Island. Conventional bombs were used during these missions.

The next phase of training began on 20 July with the first of a series of raids on the Japanese Home Islands. These missions had several purposes - they were all against locations near possible atomic bomb targets, so they helped the crews gain familiarity with those areas, they were useful general training and finally they gave the Japanese time to get used to the sight of very small formations of B-29s operating at high altitude in daytime so that the eventual attacks wouldn't stand out in advance. Twelve of these practice raids were carried out over four days, ending on 29 July.

The first atomic bomb was tested successfully at Alamogordo in New Mexico on 16 July 1945. Soon afterwards the fissionable materials for the bomb was rushed out to Tinian, where the bombs would be assembled. Some of the material was delivered by the cruiser USS Indianapolis. She dropped off her cargo on 26 July and was sunk by a Japanese submarine off Leyte on 29 July while on her way back. The rest of the material was flown out.

There was only enough material for two bombs, both of which were ready by the start of August. A list of suitable target cities had already been selected and the decision to drop the bombs had already been made. 3 August had been chosen as the earlier date for the attack, but the actual timing was dependent on the weather.

The first target was Hiroshima on Honshu. Seven B-29s was allocated to the attack. One was a spare aircraft that would be based at Iwo Jima in case of problems with the main force. Three were weather planes - one for Hiroshima and one each for two alternative targets. The bombing force consisted of three aircraft. Colonel Tibbet was to carry the bomb on the Enola Gay, while The Great Artiste and No.91 carried cameras and observers. No other Twentieth Air Force missions were to be carried out on the same day.

The Enola Gay took off at 2.45am on 6 August. The flight to Hiroshima went smoothly and the bomb was dropped at 9.15am. The aircraft then turned through 150 degrees and dived to gain as much speed and thus distance as possible. She was fifteen miles away when the bomb went off, but even at that distance felt two shocks. The crews were eyewitnesses to the resulting fireball and mushroom cloud, before heading back to Tinian, arriving at 14.58.

The plan had always been to use the second bomb quickly if the Japanese government didn't indicate a willingness to surrender. The original target date had been 11 August, but a bad weather forecast meant that the raid was brought forward to 9 August. This time there were two possible targets - Kokura, where there was a large Japanese Army arsenal and Nakasaki, with four giant Mitsubishi armament factories.

The plan was similar to that of 6 August. This time there were two weather planes, one spare aircraft and the same three-aircraft strike force. The bomb itself was to be carried in Bock's Car, flown by Major Sweeney. Some confusion was later caused by this, as Sweeney's normal aircraft, The Great Artiste, also took part in the raid, piloted by Captain Bock.

The weather interfered on 9 August. The weather planes took off at 2.30am, followed by the strike force at 3.49am. Kokura was the main target, and the attack force was heading towards that city when the weather closed in. The decision was made to attack Nagasaki instead, but even there the weather was poor. After a radar guided run-in Sweeney found a gap in the clouds and dropped the bomb at 10.58am local time. This time the aircraft felt five shocks as they flew away. The poor weather and longer than expected flight meant that the aircraft were short of fuel and so they had to land at Okinawa first, arriving at 14.00. After refueling they were back at Tinian by 23.39.

On 10 August the Japanese cabinet, prompted by Emperor Hirohito, agreed to accept the Potsdam peace terms and begin negotiations to end the war. The role of the Hiroshima bomb in this decision is clear - on 7 August Togo had advised the Emperor to end the war, but the military had resisted. On 8 August the USSR declared war on Japan and quickly overran Manchuria. On 9 August, after the Nagasaki bomb, the Emperor decided in favour of ending the war. It took the rest of the day to convince the cabinet and the message wasn't transmitted to the outside world until 10 August. The formal surrender of Japan followed on 15 August. The Nagasaki bomb may have strengthened the Emperor's resolve and weakened the more extreme supports of a fight to the death, but this isn't at all clear.

The 509th carried out one more mission, sending seven aircraft against special targets on 14 August, part of a general resumption of bombing activity after the peace negotiations appeared to have stalled. That ended the group's wartime career.

The group returned to the United States late in 1945. It gained two more bombardment squadrons in 1946, and became part of Strategic Air Command, where it formed the core of the Nuclear strike force. It was also used during the Bikini Atoll tests of July 1946.




December 1944-1949: Boeing B-29 Superfortress
1950-1952: Boeing B-50 Superfortress


9 December 1944 Constituted as 509th Composite Group
17 December 1944 Activated
April-June 1945 To Tinian and Twentieth Air Force
6 August 1945 Dropped Hiroshima Bomb
9 August 1945 Dropped Nagasaki Bomb
Oct-Nov 1945 To United States
21 March 1946 To Strategic Air Command
July 1946 Redesignated 509th Bombardment Group (Very Heavy)
July 1948 Redesignated 509th Bombardment Group (Medium)
16 June 1952 Inactivated

Commanders (with date of appointment)

Col Paul W Tibbets Jr: 17 Dec 1944
Col William H Blanchard: 22 Jan 1946
Col John D Ryan: 15 Sep 1948
Col William H Blanchard: 21 Jul 1951-16 Jun 1952.

Main Bases

Wendover Field, Utah: 17 Dec 1944-26 Apr 1945
North Field, Tinian: 29 May-17 Oct 1945
Roswell AAFld, NM: 6 Nov 1945-16 Jun 1952.

Component Units

1944-46: 320th Troop Carrier Squadron
1944-52: 393rd Bombardment Squadron

Assigned To

1945: XXI Bomber Command: Twentieth Air Force
March 1946 onwards: Strategic Air Command

How to cite this article: Rickard, J (9 June 2014), 509th Composite Group (USAAF) , http://www.historyofwar.org/air/units/USAAF/509th_Composite_Group.html

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