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Johnston Island


Photograph of 3" antiaircraft battery at Johnston Island

U.S. Marine Corps. Via ibiblio.org

Johnston Island (169.53W 16.73N) is little more than a large sand bar in an otherwise empty patch of ocean, 720 miles (1160 km) southwest of Pearl Harbor. It is the only significant island in an atoll 9.3 miles (15 km) long and 2.5 miles (4 km) wide. The island itself originally measured 1000 by 200 yards (900 by 180 meters) for an area of only 64 acres (24 hectares) but was substantially enlarged through coral dredging during the war and after. The island is nearly flat with little vegetation and is surrounded by shallow water with numerous coral heads except to its south.  Rainfall averages 24 inches (61 cm) a year and temperatures stay within the range of 70-80 F (20-30 C) year round.

The atoll has a large underwater shelf to leeward that can anchor large numbers of vessels, but there is no meaningful protection from storms or submarines.  Nevertheless, some facilities were constructed, beginning in 1934. A ship channel was dredged into the lagoon and the dredgings used to create an artificial island, 300 by 800 feet (90 by 240 meters) to the northeast of Johnston. This was used as a seaplane parking area. Three seaplane lanes were also dredged. In September 1941 the island was enlarged by filling in a 200 by 2500 foot (60 by 760 meter) on its south shore, which made the island large enough for a 4000 foot (1200 meter) runway.

When war broke out, Johnston was garrisoned by a small detachment of 1 Marine Defense Battalion (162 men) with two 5" coastal guns and four 3" antiaircraft guns. A Seabee detachment arrived in July 1942 and dredged additional seaplane runways, using the dredgings to expand the island again to make room for a second 3500 foot (1100 meter) runway. By 1944 the main runway had been expanded to 6000 feet (1800 meters) and the island had grown to 160 acres (65 hectares).

Postwar the island was used for nuclear testing and storage of chemical weapons, for which its location distant from any inhabited island or sea lane but within reasonable travel distance from Hawaii made it ideal. It eventually reached a size of 625 acres (255 hectares) through continued dredging.

References

Huie (1944)
Rottman (2002)



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