These operations of the P-51s and P-61s had been made possible by the early development of the airfields for which the battle of Iwo Jima had been fought. Along the central plateau of Iwo the Japanese had laid out three airfields, sometimes called, from the neighbouring village, Montoyama No. 1, No. 2, and No- 3 or simply South, Central, and North fields. The first had two strips, 5,025 and 3,965 feet (1532 and 1209 meters) long. Central Field had two runways, 5,225 and 4,425 feet (1593 and 1349 meters), built in the form of an X. The third, with a single strip, never became operational. The basic plan (WORKMAN) for the development of Iwo into an air base, drawn up in October, contemplated the use where possible of existing Japanese facilities, and although the whole complex was to serve primarily as a very long range base, the most pressing job was the rehabilitation of some strips for local fighter use. The WORKMAN schedule, a Navy responsibility, was as follows: at No. 1, one 5,000-foot (1524 meter) runway was to be rehabilitated for fighter operations by D Plus 7; at No. 2, the northeast-southwest runway was to be repaired for fighter use by D plus 10 and the east-west runway extended into a 6,000-foot (1829 meter) fighter strip by D Plus 50; later, by D plus 110, the northeast-southwest runway was to be extended to 8,500 feet (2591 meters) for B-29s and a second 8,500-foot runway was to be built parallel to the first; at No. 3, one 5,000-foot runway was to be ready for fighters by D plus 50.

All runways were to be 200 feet (61 meters) wide. Construction was assigned to Commodore R. C. Johnson's 9th Naval Construction Brigade, made up of the 8th and 41st Naval Construction Regiments and one AAF unit, the 811th Engineer Aviation Battalion. The 8th Regiment was assigned to general construction, the other units to work on the airfields.

Three Seabee units went in with the assault troops on D-day to serve as shore parties and to begin work on the airfields as they were overrun. Determined enemy opposition upset the construction schedule but as the fields were captured, runways were rapidly made serviceable for minimum operations. One strip on South Field was being used by observation planes as early as 26 February (D Plus 7), and by 2 March the other strip was graded to 4,000 feet (1219 meters). On the 4th, DETACHMENT paid its first dividend when a B-29 in distress came in for an emergency landing. Two days later the P-51s came up from Saipan, and from then on, South Field was in constant use while construction was continued. Although work at Central Field was held up by the protracted land battle, on 16 March it too was operational, with one strip graded to 5,200 feet (1585 meters), the other to 4,800 (1463 meters).

On that day, Colonel William E. Robinson, staff engineer for XXI Bomber Command, landed at Iwo Jima to survey the possibilities of B-29 base development. From the point of view of B-29 crews, Iwo's chief importance was that it would make fighter escort possible and serve as a haven for bombers in distress. But the planners had been interested also in its use as a staging base by which the tactical radius of the B-29 could be lengthened or its bomb load increased. It was for combat-loaded Superforts that the 8,500-foot (2591 meter) runways had been designed, and the WORKMAN plan had provided facilities for 60 to 90 of the bombers. Robinson was convinced that North and Central Fields could be built to serve as many as 150 B-29s, and after his return to Guam, he gave LeMay an amended base development plan. LeMay approved it on the day it was submitted, 26 March, as did Major General Willis H. Hale, who since Harmon's death had been serving as deputy commander of the Twentieth. Major General James E. Chaney, Saipan's island commander, and Admiral Hoover readily concurred, so that by 4 April Robinson had carried the plan to Oahu where Admiral Nimitz gave his final approval. In Robinson's plan, North and Central fields were to be combined into one huge airdrome covering over 4 square miles (10.4 square kilometres) (half the surface of the island), with two B-29 runways, 9,400 and 9,800 feet (2865 and 2987 meters) long, and a 5,200-foot (1585 meter) fighter strip.

The engineers found the task of building airfields on Iwo Jima complex and often exasperating. Iwo, which had risen from the sea within the memory of living men, was still a semiactive volcano, and in many places sulphur-laden steam issued from crevices. Some areas that were honeycombed with steam pockets had to be avoided when runways or subsurface gasoline lines were laid out. Although the volcanic ash which covered the island's surface worked more easily than the coral to which Pacific engineers were accustomed and could be readily compacted to sustain B-29 loads, when wet it eroded easily if compacted, and asphalt could be laid on an ash base only when dry. Unfortunately, heavy rains in the spring months delayed construction by keeping the surfaces wet for as much as a week at a time.

Even in good weather progress on the B-29 runways lagged, until in April the Seabees began working two ten-hour shifts a day and reduced drastically the effort devoted to construction of their own housing and other secondary facilities. In June the program suffered a setback when an asphalt area of approximately 80,000 square feet (7432 square meters) at Central Field was ruined by water penetrating the subbase; on another occasion it was necessary to remove the crushed stone and subgrade from some 1,500 feet (457 meters) of asphalt runway.

ATLANTIC OCEAN: At 0920, the Inger Toft in Convoy RU-156 was torpedoed and sunk by U-722 3 miles 270° from Neirst Point, Isle of Skye. The master and 29 crewmembers were picked up by armed trawler HMS Grenadier and landed at Loch Ewe.

The Coast Guard-manned destroyer escorts USS Lowe, Menges, Pride, and Mosely, which comprised Task Group 22.14, located the submerged German submarine U-866 off the coast of Sable Island and sank it with a loss of all hands.