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The Marianas Islands are an island arc located
about 1400 miles (2250 km) south of Japan.
There are 15 islands in the chain, which extends about 425 miles (684 km) from
Farallon de Pajaros in the north to Guam
in the south. Most are mountainous, with elevations up to 2585' (788
meters). The islands have a total area of 402 square miles (1041
km2), of which over half (225 square miles or 583 km2)
is from Guam alone. The islands have relatively fertile soil and are
covered with mixed scrub and grassland, with a few mangrove swamps. Beaches tend to be narrow and backed by coral cliffs and there are reefs off many of the shore lines.
Because they are located in the deep Pacific ocean basin, the islands have no sedimentary basement complex and no interesting mineral resources. However, they have a good climate for the cultivation of sugar cane, and supplied much of Japan's sugar. They are also strategically located along Japan's sea lanes to the Mandates.
In late 1941, the southernmost of the
had been a U.S.
possession since the Spanish-American War of 1898.
The remaining islands belonged to Japan, which had seized them from Germany
in October 1914, during the First World War, and developed them for sugar production
under the auspices of the South Seas Development Company. By the time
war broke out in the Pacific, the Japanese population of the islands
outnumbered the indigenous
population (Chamorros) by two to one.
specified that these islands were not to be fortified, but with the
the treaties in the early 1930's Japan proceeded to build
large airfields on Saipan, within easy range of Guam. The
United States neglected the
fortifications on Guam, which was considered too exposed to be held in
event of war. Japanese troops landed on Guam just two
days after the attack on Pearl
Harbor and easily conquered the island.
The Marianas were identified as an important
objective in prewar planning (Plan ORANGE), but it was not until August
1943, at the QUADRANT conference, that a formal decision was made to invade the Marianas
following the seizure of the Palaus.
In December 1943, at the SEXTANT conference, the U.S. Army Air Forces
forcefully argued for an early invasion of the islands so that they
could be used as bases for the strategic bombing of Japan
by B-29 Superfortresses.
Seizure of the Marianas would also open a number of options to the Allies, since bases here would
be within range of Palau, the Philippines, Formosa, or the Bonins. Invasion of the
Marianas was given priority over the Palaus. However, the target date
of 15 June 1944 was not set until 12 March 1944, and Nimitz assigned FORAGER to 5 Fleet (Spruance) on 28 March.
Turner had already
begun planning by that date. About a week before 5 Fleet received its
formal directive, Turner had concluded that Saipan should be invaded
first. Saipan had the best airfields, and its capture would cut off the
islands to the south. Turner divided his force into a Northern Force
under his personal command for the landings on Saipan and Tinian, and a
Southern Force under Conolly
for the Guam invasion. The assault elements for Northern Force would be
provided by 2
Marine Divisions under Holland
Smith and the assault elements for Southern Force would be provided
Marine Division and 1
Provisional Marine Brigade under Geiger.
The floating reserve under Blandy
would consist of Ralph Smith's
and the invasion would be covered by the fast carrier forces under Mitscher and land-based aircraft under Hoover. Lockwood's submarines would scout well to the
west while logistical support
would be provided by Calhoun's
carriers struck the
Marianas repeatedly, beginning on 23 February 1944. This was the first
good look at the Marianas in over two years, and the raiding aircraft
a wealth of photographic intelligence.
The raid also destroyed 168 Japanese aircraft and sank 45,000 tons of shipping. Land-base
aircraft of 5,
7, and 13 Air Forces,
mostly heavy bombers
conducting night raids, bombarded Japanese bases in the Carolines throughout March
to ensure there would be no Japanese interference with FORAGER from the
south. Starting on 18 April, photoreconnaissance
aircraft (B-24s) from VD-1, VD-3, and VMD-254 from Guadalcanal began staging through
Eniwetok to map the Marianas.
These were joined by VD-4
based on Eniwetok itself.
Preinvasion strikes began on 11 June. These came as a rude shock to the Japanese, who had not imagined that the Americans could exploit their successes in the Marshalls and against Truk so quickly, and who in any case believed the Palaus would be the next target. The Americans had also carried out an extensive deception campaign, WEDLOCK, to suggest the next assault would come in the Kuriles. The initial fighter sweeps took place in the afternoon in an attempt to achieve tactical surprise, since previous invasions had begun with dawn raids.
Landings commenced on 15 June on Saipan, but landings scheduled for the next day on Guam were postponed when the Japanese carrier fleet was spotted by the American submarines. The Battle of the Philippine Sea ended on 20 June with a decisive American victory. Saipan itself fell on 9 July after a hard-fought campaign.
Landings began on Guam on 21 July and on Tinian on 24 July. The Americans secure Tinian on 1 August and Guam on 10 August.
Once in American hands, the airbases
on Saipan were
expanded, and new strategic
air bases were built on Tinian.
These airbases brought the B-29
within range of the Japanese home islands. It was from Tinian
that the B-29s carrying the first nuclear weapons
were launched against Japan.
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