Metfield was built in 1943 as a standard Class-A bomber base with three intersecting concrete runways, fifty dispersal points, and two T-2 hangars. Construction required closing the B1123 road between Halesworth and Harleston. The buildings to house its 2,900 personnel sprawled across former farmland to the southwest. The airfield was assigned to the United States Army Air Forces Eighth Air Force and given the designation USAAF Station 366. It was one of the most isolated Eighth Air Force fields in Suffolk, surrounded by countryside rather than other military activity.

The first American occupants arrived on 3 August 1943: the 353rd Fighter Group, flying Republic P-47D Thunderbolts. They painted their aircraft with black, yellow, black, yellow spinners and a striking 48-inch black and yellow check band around each cowling, all the way back to the exhaust stubs. The 353rd was the fourth P-47 unit to join the Eighth Air Force, and from Metfield they flew counter-air sweeps over France and the Low Countries, escorted bombers to targets in western Europe, and dive-bombed German positions in France. On 12 April 1944 they moved on to RAF Raydon, and the field became a heavy bomber station.

The 491st Bombardment Group (Heavy) flew its Consolidated B-24 Liberators into Metfield in late May 1944, the last aircraft arriving on the 30th. Their tail code was a Circle Z. The squadrons, the 852nd, 853rd, 854th, and 855th, had been recruited unusually, with ground crews drawn from other stations across the 2nd Air Division. They began combat on 2 June, just in time to hammer airfields, bridges, and coastal defenses before and during the Normandy invasion. After D-Day they ranged across Germany, hitting Berlin, Hamburg, Kassel, Cologne, Gelsenkirchen, Bielefeld, Hannover, and Magdeburg. Once they bombed the headquarters of the German General Staff at Zossen. On 15 August 1944 the 491st was reassigned to RAF North Pickenham.

After the 491st left, a strange new tenant arrived. The 1409th Army Air Force Base Unit took over some of the B-24s, operating them alongside Douglas C-47 Skytrains and C-54 Skymasters under the command of the European Division of Air Transport. Their mission was classified: clandestine transport runs to neutral Sweden, flying out special materials and ferrying personnel. They also used RAF Leuchars in Scotland as an advanced base. On 4 March 1945, during the Luftwaffe's nighttime intruder mission Operation Gisela, a Junkers Ju 88G-6 strafed Metfield, killing one man in the control tower. The German night fighter had been trying to attack an inbound B-24 with its Schrage Musik upward-firing cannon and crashed just south of the airfield.

The 1944 explosion left a crater so large that an entire loop road had to be built to bypass it. For years afterward, the crater filled with water, becoming a lake that locals used as a dump for discarded equipment. When it was finally drained and cleaned, divers found everything from cookware to several unexploded bombs. Fragments of the 1944 ordnance still surface in the surrounding fields. The airfield itself was abandoned in May 1945 and sold off in 1964 and 1965. Today only a few brick buildings, some deteriorating Nissen huts, and concrete taxiway remnants suggest that 2,900 Americans once lived and fought from this quiet patch of Suffolk farmland.