1943

First Lieutenant Lawrence F. O’Neill of the 342nd Fighter Squadron, in the cockpit of his P-47D Thunderbolt following his quadruple victory on 26 December 1943^{[lower-alpha 2]}

Group P-47D Thunderbolt^{[lower-alpha 3]}

Group P-47D Thunderbolt^{[lower-alpha 4]}

After an extended period of training in the northeast United States, the personnel boarded the Army transport ship Henry Gibbons and left the wharf at Weehawken, New Jersey on 15 May 1943. They groups personnel all thought they were heading for the European theatre of war. However, they went through the Panama Canal instead and crossed the Pacific Ocean reaching Brisbane, Australia on 14 June 1943. They moved to Archer Field (Archerfield airfield) and waited for their aircraft to arrive.

The group's P-47D Thunderbolts began to arrive in Brisbane in the same month, and by the end of July after they had "run in" their engines on local training flights, the group began long-range missions to strike at Japanese targets in New Guinea. In mid-June the 348th's three squadrons (340th, 341st, 342d) made the 1,200-mile flight from Brisbane to Port Moresby, New Guinea. The group operated from New Guinea and Noemfoor until November 1944, flying patrol and reconnaissance missions and escorted bombers to targets in New Guinea and New Britain. The 460th Fighter Squadron, stationed at Noemfoor, New Guinea, was also later attached to the 348th Fighter Group on 23 September 1944 .

The arrival of the 348th as the first P-47 group in the Southwest Pacific area coincided with the opening of the Allied offensive in New Guinea. During the summer of 1943 the P-47 missions were chiefly as cover for bombers in the Lae-Salamaua area, and for transports carrying supplies to the new mountain locked airstrip at Tsili, only a few miles from the Japanese held Markham Valley. The group met its first air combat over Tsili on 16 August 1943, when two squadrons tangled with the fighter cover of an enemy bomber formation, and shot down three aircraft.

In September the 348th's planes provided cover for the paratroop landing at Nadzab in the Markham valley, and with the capture of Nadzab and Lae the group entered into one of the most spectacular phases of its overseas career, in a series of fighter sweeps, generally by flights of four planes, over the Japanese stronghold of Wewak.

Lieutenant Colonel Neel Kearby, the Commanding Officer of the 348th Fighter Group shot down his first Japanese aircraft on 4 September 1943. He shot down a second aircraft on 15 September 1943. Colonel Kearby was awarded the Medal of Honor for action over New Guinea on 11 October 1943. After leading a flight of four fighters to reconnoiter the enemy base at Wewak, Lt Col Kearby sighted a Japanese bomber formation escorted by more than 30 fighters. Despite the heavy odds and a low fuel supply, and although his mission had been accomplished, Kearby ordered an attack, personally destroying six of the enemy planes. For covering Allied landings and supporting ground forces on New Britain, 16–31 December 1943, the group was awarded a Distinguished Unit Citation.

1944

In 1944 the group began to attack airfields, installations, and shipping in western New Guinea, Ceram, and Halmahera to aid in neutralizing those areas preparatory to the US invasion of the Philippines. The group's pilots shot down 100 Japanese planes without the loss of a single pilot in aerial combat. From Finschhafen the group flew its first fighter-bomber missions. In the early spring of 1944, while the group was at Saidor, fighter-bomber work began in earnest with attacks on the Japanese concentrations in the Hansa Bay region just ahead of the advancing Australian troops

After 18 months in New Guinea the 348th boarded ship and plane for the Philippines. One squadron, the 460th, arrived several weeks before the other three, and proceeded to roll up an imposing score of enemy planes, shipping, and personnel destroyed, providing cover for convoys, flying patrols, escorted bombers, attacked enemy airfields, and supporting ground forces. During a three-week period it sank 50,000 tons of enemy shipping, which was slightly more than one-tenth of all the shipping sunk by the entire Fifth Air Force during the year 1944. On 10 November the 460th squadron deployed forward to Tacloban Airfield on Leyte, simultaneously escorting a group of B-25 bombers attacking a convoy loaded with an estimated 10,000 enemy troops en route to reinforce the Japanese army on Leyte. The squadron's planes were the first of the Army Air Force to fly over occupied Manila after the Japanese capture of the Philippines. A flight led by Colonel Dunham, made the first return flight on 17 November 1944.

The group's greatest day, in point of total of enemy planes destroyed, was 14 December 1944 when, in protection of the invasion fleet heading to Mindoro, 5 Japanese planes were shot down, an estimated 75 were destroyed and 20 more damaged, on the airfields of Negros Island only a few minutes flight from the Allied invasion force, which landed on Mindoro the following morning.

In aerial combat at the 348th's best day came on 24 December 1944 when its planes escorting B-24 Liberator heavy bombers in one of the first bomber strikes on Clark Field, met an attempted interception by an estimated 100 Japanese fighters. 32 of the enemy aircraft were definitely destroyed, 7 probably destroyed, the remainder were driven off, and the bombers proceeded undamaged to carry out their mission.

Early in December 1944, while the group's planes were operating from Taoloban strip, the majority of group personnel were camped inland near Burauen when the Japanese landed several hundred paratroops on an uncompleted airstrip less than a quarter of a mile from the group's camp, cutting the only road leading from the camp. For several days the camp was isolated between the paratroops on the East and the Japanese patrols on the West. Two men on guard post were surprised and killed by an enemy patrol, but the camp defense's prevented any breakthrough and the paratroops were finally wiped out by infantry and tanks.

When U.S. troops landed on Luzon the 348th, now in process of conversion from P-47's to North American P-51 Mustangs, began operation from San Marcelino airstrip a few days after the landing at San Marcelino and Subic Bay. From this location the unit entered upon what many of its members consider its most outstanding work of the war, bombing and strafing in close support of ground troops. This work lacks the excitement and glamor of serial combat, or even of bombing and strafing of seen targets. Bombs and bullets are poured into areas where the enemy is reported to be, and day after day the mission reports stated "Results unobserved due to foliage". Only rarely were advancing ground troops able to tell what part of the damage found was done by a particular air strike.

1945

At the time the 348th began ground support operations from San Marcelino, the infantry had taken Subic Bay and Olongapo and had started east with the objective of sealing off Bataan so that the Japanese, retreating southward from Lingayen, could not use the Bataan Peninsula's defensive strength as did the U.S. forces in 1942. However, a few miles East of Olongapo stubborn Japanese resistance suddenly had been met in Zigzag Pass, where the road climbed in a series of hairpin turns overlooked by the enemy's positions. Our ground forces had suffered some casualties, had dug in, and in four days had been unable to make any appreciable gain.

342d Fighter Squadron P-51D Mustang in 1945^{[lower-alpha 5]}

Second Lieutenant Stanley E. Michalowski, 342nd Fighter Squadron, standing by his P-51D Mustang, Ie Shima, Japan, August 1945.

On Leyte the 348th had done experimental bombing with a new and highly effective firebomb weapon, and it was proposed that it be used to break the deadlock in Zigzag Pass. However the infantry division occupying the west end of the pass was uncertain about the use of the bomb in close support of their troops, for fear of inaccurate bombing. So a Japanese supply area, well back of their front line, was bombed as a demonstration of accuracy, and was left neatly blanked with flame. There was no further lack of confidence. American infantry proceeded to direct our pilots to bomb and strafe just ahead of their front line, and for seven days advanced steadily until their mission of scaling off the Bataan Peninsula had been accomplished.

Occasionally the curtain of "unobserved results" would lift. One strike, directed by Filipino guerrillas who set off smoke pots to mark tan enemy bivouac area, was later found to have caused 700 Japanese casualties.

After another strike west of Fort Stotsenburg, ground troops were able to move in quickly and found 574 Japanese, all killed by the single air attack. Neigher of those missions involved more than 32 sorties and 30 missions a day. It would be impossible to estimate how many other thousands of enemy dead were covered with the phrase "results unobserved".

During the month of April 1945 the 348th net a record for tonnage of bombs dropped on the enemy, with a total of 2091.5 tons. Total ammunition expended was just under two million rounds. So far as is known, this bomb tonnage is the greatest every dropped in one month by any group, either fighter or bomber, and the accuracy of the bombing attested repeatedly by reports from ground observers. Most of the record tonnage was dropped in the Ipo Dam area northeast of Manila, and helped pave the way for the infantry's capture of that vital control-point of Manila's water supply. From San Marcelino the 348th also flew missions over French Indochina, Hainan, China, and Formosa.

In May 1945 the group moved to Floridablanca airfield, west of Fort Stotsenburg, and from there continued attacks on Japanese ground troops, chiefly in the Cagayan Valley in northern Luzon. By the middle of June the enemy forces had disintegrated and scattered so that profitable targets were hard to find, So operations of the 348th were redirected to the Ryukyus, and the group began operations from Ie Shima in mid-July.

Contrary to expectations the Japanese air forces did not choose to fight, and in the following month only 15 enemy planes were shot down without loss to the 348th in air combat. However, there was an abundance of ground and shipping targets in Kyūshū and North China, and the group's P-51s took a constant toll of enemy transportation on water and land before the afternoon of 14 August when the planes of the 348th delivered the last bombs dropped on Japan before the order was given to "cease firing".

In the immediate postwar era, the group moved to Itami Airfield, Japan in October 1945 as part of Far East Air Forces, performing occupation duty. The 348th Fighter Group was inactivated at Itami Airfield on 10 May 1946.