In 1944 it converted to Boeing B-29 Superfortresses and saw combat in the Pacific during World War II, where it was awarded a Distinguished Unit Citation for its actions during the strategic bombing campaign against Japan.

It became part of Strategic Air Command (SAC) during the Cold War, maintaining a portion of its strength on alert.

It remained quarantined until 21 December when it was cleared by the medical department to move to the Aviation Concentration Center, Garden City, Long Island, arriving on the 23d.

The 21st's efficiency was commented on by the post commander when a record was established with 69 launches on one day, with several hundred hours of flying recorded.Training was given to many members of the pursuit squadrons of the First Army Air Service as they arrived in France; and beginning in August 1918, to new pilots for the planned Second Army Air Service as they began to arrive for training.

[5] At the time of the Armistice on 11 November, the men of the 21st Aero Squadron remained on duty completing the training of the pilots assigned to Field #3.

The 21st, therefore, remained at Issoudun until January 1919 when orders were received to proceed to the 1st Air Depot, Colombey-les-Belles Airdrome, France, for demobilization.

From Colombey, the squadron moved to a staging camp under the Services of Supply at Bordeaux, waiting for a date to board a troop ship for transportation home.

[7] The 21st Observation Squadron (Long Range Amphibian) was activated on 1 March 1935 at Bolling Field, District of Columbia and was assigned to the 2d Wing.

[2] The 21st Observation Squadron flew light reconnaissance aircraft in support of Army maneuvers primarily in northern Virginia.

It moved to the 36th Street Airport, Miami, Florida, where it was attached to the Navy and began to fly Neutrality Patrol, sea search, and weather reconnaissance missions.

[2][7] After the attack on Pearl Harbor the squadron remained in south Florida flying antisubmarine patrols against any German U-boats approaching the United States coast.

[2] At Gowen, the squadron was an Operational Training Unit (OTU), first with Boeing B-17 Flying Fortresses and, after 1943, with Consolidated B-24 Liberators.

[9] The OTU program involved the use of an oversized parent unit to provide cadres to "satellite groups" prior to their deployment overseas.

[10] However, the Army Air Forces found that standard military units, based on relatively inflexible tables of organization, were proving less well adapted to the training mission.

Accordingly, it adopted a more functional system in which each base was organized into a separate numbered unit,[11] while the groups and squadrons acting as RTUs were disbanded or inactivated.

[14] The squadron was activated again on 1 June 1944[4] as part of the new 502d Bombardment Group (Very Heavy), which was being organized at Davis-Monthan Field, Arizona.

[16] After completing training the squadron deployed to the central Pacific and became part of XXI Bomber Command at Northwest Field (Guam) for operational missions.

[15] It flew its first mission against the Japanese home islands on 15 July 1945 against the oil refinery at Kudamatsu[17] and afterwards operated principally against the enemy's petroleum industry.

The squadron earned a Distinguished Unit Citation for August 1945 attacks on the coal liquefaction plant at Ube, a tank farm at Amagasaki and the Nippon Oil refinery at Tsuchizaki.

The squadron was equipped with first generation Boeing KC-135A Stratotankers as part of the 4241st Strategic Wing, a dispersed Strategic Air Command (SAC) Cold War wing formed to spread SAC's Boeing B-52 Stratofortress heavy bombers over a larger number of bases, thus making it more difficult for the Soviet Union to knock out the entire fleet with a surprise first strike.

[2] Starting in 1960, one third of the squadron's aircraft were maintained on fifteen-minute alert, fully fueled and ready for combat to reduce vulnerability to a Soviet missile strike.

[2] During 1959 it participated in tests to determine the compatibility of the KC-135 with the refueling systems of the North American F-100 Super Sabre, McDonnell F-101 Voodoo, Lockheed F-104 Starfighter, Republic F-105 Thunderchief and Douglas B-66 Destroyer aircraft.

[20] In early 1960, the 4241st wing deployed its operational squadrons during the reconstruction of the Seymour Johnson runway and main taxiway.

[25] Beginning on 1 May 1972, the 911th deployed to Andersen Air Force Base, Guam and was attached to the Strategic Wing, Provisional, 72.

During the 1991 Gulf War, aircraft and crews from the squadron deployed to Lajes The Azores; Rota and Zaragoza and were attached to the 1709th Air Refueling Wing (Provisional).

From June through August 2000 the squadron moved its operations to MacDill Air Force Base, Florida while the runways at Grand Forks were being repaired.

From the start of air operations over Afghanistan 7 October to 2 November 2001 the 319th had flown over 150 sorties and more than 1050 hours; pumping over 1.4 million US gallons (5,300 m3) of gas into more than 450 planes.