US Navy Base Construction on Iwo Jima During World War II
Iwo Jima, the largest island of the Volcano group, is about five miles long and two and one-half miles wide at its broadest point. The most prominent feature is Mt. Suribachi, a volcanic cone rising to nearly 550 feet at the southern end of the island. The northern half of the island forms a broad dome, with maximum elevations of 340 to 387 feet. Iwo has enough flat land in its 8 square miles for the construction of airstrips. The entire shore is rugged and precipitous, with few good landing-beaches. The Japanese took advantage of the terrain and developed Iwo Jima into an air base, two fields being operational and a third under construction at the time of the American assault. The southernmost field had two strips, 5,025 and 3,965 feet long, respectively. Two runways, forming an X, had been built to 5,225 and 4,425 feet in length, near the center of the island. A third strip, 3,800 feet long, had been started farther north. These three fields, the main objective of the assault, became the nucleus for the development of an advance air base for United States aircraft.
The assault on Iwo Jima was initiated on February 19, 1945, by the Fifth Amphibious Corps and the Third, Fourth, and Fifth Marine Divisions. Three Seabee units, the 31st, 62nd, and 133rd Battalions, were assigned to the Marines during the assault, to act as shore parties and to start work on the airstrips at the earliest possible moment.
The Marines went ashore on the southeastern beaches of Iwo Jima, meeting relatively little resistance. However, the enemy, taking advantage of the hilly terrain, soon concentrated extremely heavy artillery and mortar fire against the Marine positions. By the evening of D-day, the Marines had cut across the narrow isthmus to the west shore of the island, isolating the southern airfield, which was captured the following day. By February
26, the northeast-southwest Japanese runway had been made operational by the Seabees and was in use by observation planes.
The Marines continued their painful advance toward the northern tip of the island and by March 3 had captured all three airfields. On that date, transports began operating from South Field to bring in much-needed supplies and to evacuate the wounded. Effort was concentrated on the rehabilitation of the northeast-southwest 5,225-foot strip which had been constructed by the Japanese at Central Field. By the time Iwo Jima was secured on March 16, both South and Central Fields had one operational strip, and 50 Superfortresses had made emergency landings on their return from great incendiary raids over Japan.
With the close of the assault phase of operations, attention was turned to the execution of plans for the development of Iwo Jima as an important air base. The Ninth Construction Brigade was organized for this purpose. The Eighth Regiment, consisting of the 8th, 90th, 95th (Section Two), and the 23rd Special Battalions, and the 41st Regiment, composed of the assault battalions, made up the brigade.
Initial plans called for the development of three airfields, to be known as South, Central, and North Fields, on the sites of the existing Japanese strips. The 5,025-foot strip at South Field was to become a 200-by-6,000-foot fighter strip. The longer runway at Central Field was to be extended to 8,500 feet for B-29 operations, and a similar strip was to be constructed parallel to it. In addition, the second strip at Central Field was to be extended to 6,000 feet. North Field, where the Japanese had only started construction, was to have one 200-by-5,000-foot strip for fighter operations.
At South Field, the temporary strip was rebuilt and additional taxiways, shops, and service areas were constructed while the field was in constant operation. On April 7, 1945, fighters took off from South Field to form the first land-based fighter escort for B-29's on a strike against the Japanese homeland. By July, the runway had been extended to 6,000 feet and had been surfaced with emulsified asphalt. Also constructed were 7,940 feet of taxiways and 258 hardstands.
By July 7, 1945, the first B-29 strip at Central Field had been paved to 8,500 feet and placed in operation. During the day, 102 B-29's, returning from a raid on Japan, landed on the field. Several subgrade failures occurred in the construction because of ground water and soft spots in the subgrade. In some places the paving sealed off steam which had been generated below the surface. When the steam condensed, the subgrade became saturated. At one time, poor subsoil under the paving made it necessary to remove about 1,500 feet of crushed stone and subgrade. By July 12, the B-29 strip had been completed and paved for a length
of 9,800 feet. The east-west runway was developed into a fueling strip, 6,000 by 570 feet, with 60 fueling outlets. The second B-29 strip had been graded to 9,400 feet by V-J day, and was left unpaved.
Virtually the entire job at North Field was new construction in rough terrain which consisted principally of consolidated volcanic ash. The initial portion of the work in preparing the subgrade for the strip entailed the moving of about 200,000 cubic yards of rock and volcanic ash. Seabee construction was stopped on April 27, and the project was turned over to an Army Engineer battalion for completion. By V-J day a strip, 6,000 feet long, had been graded and was paved to 5,500 feet; 10,000 feet of taxiways had been graded; and 129 fighter hardstands had been provided.
All facilities on Iwo Jima were constructed to support the air base. Main projects were tank farms, water-distribution system, roads, hospitals, storage areas, and waterfront facilities.
A temporary tank farm, consisting of four 1,000-barrel tanks--two for aviation gasoline, one for motor gasoline, and one for diesel oil--was ready for operation on March 16, 1945. Dismantling of this farm began when the permanent farms were placed in operation. The permanent tank-farm system consisted of two central farms, called East and West Farms, and small farms at each of the three airfields. Small installations provided 1,000 barrels of aviation gasoline for South Field; 6,000 barrels for Central Field; and 6,000 barrels for North Field. The East Tank Farm, for aviation gasoline only, had a capacity of 80,000 barrels. West Farm facilities consisted of 160,000 barrels for aviation gasoline, 50,000 barrels for motor gasoline, and 20,000 barrels for diesel oil.
All unloading of cargo at Iwo Jima was across the beaches. Berthing was later developed at both eastern and western beaches, the latter proving much more satisfactory. Stevedoring was extremely difficult because of the heavy surf, bad weather, and sand conditions on the beaches. During the assault, marston mat was extensively used to make possible the landing of wheeled vehicles.
Harbor development consisted of a breakwater of blockships on the east side of the island and a small boat pool on the west side. A storm wrecked the blockship breakwater, and no further attempt was made to provide seaward protection for ships.
A project of high priority was the provision of a water-supply system. There are no perennial streams on Iwo and the water table lies at a considerable depth near the center of the island. A fresh-water lens, extending about 9 feet above sea level, had formed, and wells were drilled to secure water from this lens. The Japanese had dug 14 wells, eight of which were used in the development of the water system. In addition, the Japanese had paved catchment-areas which were drained into cisterns excavated in the soft rock. The runoff from the two completed airfields had been stored in masonry and concrete reservoir, which were repaired by the Seabees and became the basis of the water system. By V-J day, the system was only
half finished, with 58 small stills and eight drilled wells.
Establishment of storage areas for the ordnance, quartermaster, medical, engineering and chemical warfare departments involved the construction of quonset huts, frame buildings, and open-storage areas, as well as 27,000 cubic feet of refrigerated storage space.
Housing and messing facilities for 37,000 officers and men were set up, in addition to the individual battalion camps. Tents were used for living quarters, and quonset huts were provided for headquarters and mess halls. Medical facilities were provided at the 38th Field Hospital, the 41st Station Hospital, and the 232nd General Hospital, with a total capacity of 1,250 beds. There were also 105 beds in Navy dispensaries.
The first Seabee road construction involved the hacking of a road up Mt. Suribachi to install radar equipment. The Japanese had made no attempt at this construction. After a demolition team had cleared the terrain of mines and booby traps, a bulldozer blazed a trail to the top, and within twelve days, graders, scrapers, and dump trucks had completed the road.
To link the various activities on Iwo Jima, 20 miles of primary and 40 miles of secondary roads were constructed.
Source: Building the Navy's Bases in World War II: History of the Bureau of Yards and Docks and the Civil Engineer Corps, 1940-1946 vol.2. (Washington, DC: US Government Printing Office, 1947): 370-373.