Bombarding the Marianas: joint fires at the strategic, operational and tactical levels

FA Journal,  May-August, 2002  by Prisco R. Hernandez

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The war was lost when the Marianas were taken away from Japan and when we heard the B-29s were coming out... we had nothing in Japan that we could use against such a weapon.

Prince Naruhiko Higashikuni

Commander-in-Chief of Japanese Home Defense

"Campaign in the Marianas"

United States Army in World War II: The War in the Pacific, Phillip A. Growl

The campaign to capture the Mariana Islands from the Japanese is especially worthy of close study by the joint fire support planner because it was a campaign dominated by the employment of fires at all levels of war: strategic, operational and tactical. It was fought to capture airstrips from which to carry on a campaign of strategic bombing against the Japanese homeland.

Operational success was ensured by the neutralization of the Japanese anchorage and naval airbase at Truk and the defeat of a strong counterattack by a Japanese carrier task force. At the tactical level, the amphibious assaults were made possible by extensive preparatory bombardments and the constant application of joint firepower to support land operations. Thus, the application of strategic firepower against the enemy was the ultimate goal of a campaign that was won by the use of joint fires at the operational and tactical levels.

Strategic Environment and Operational Planning. By spring of 1944, the course of the Pacific War had turned against Japan. Powerful Japanese fleets had been fought to a standstill at Midway and the Coral Sea, and Japanese island garrisons in the South and Central Pacific had been overcome and annihilated by American and Australian forces. Furthermore, American land-based and carrier-based aircraft were routinely bombing Japanese forward anchorages, such as Rabaul and Truk. American submarines also were roaming freely, interdicting Japanese sea lines of communications by attacking military and commercial cargo shipping.

The two-pronged advance by General Douglas McArthur and Admiral Chester W. Nimitz, which started as a compromise born out of interservice rivalry, had actually became a source of strategic strength. It already was eroding Japan's limited capabilities and keeping its leadership off balance. (1)

By 1944, General McArthur had won presidential approval for his "return" to the Philippines. (2) However, the Commander-in-Chief in the Pacific Theater, Admiral Nimitz, persisted in the belief that a thrust through the small atolls and islands of the Central Pacific would shorten the war at less cost to the United States. Such a thrust would cut Japanese lines of communications to the strategic resources of Southeast Asia and defeat the Japanese Navy, thus isolating Japanese army units in the Philippines and on the Asian mainland.

This approach also was favored by General "Hap" Arnold and the Army Air Forces (AAF). The capture of airstrips in the Marianas would place the AAF in a position to launch long-range strategic bombing attacks on the Japanese homeland and interdict the north-south sea lanes that linked Japan to its sources of oil, foodstuffs and raw materials in the Philippines and Southeast Asia. (3)

By this stage of the war, United States forces had acquired a wealth of practical experience in the conduct of amphibious operations. Beginning with the campaigns for Guadalcanal, New Guinea and the Solomons in the South Pacific and the Gilberts and Marshalls in the Central Pacific, all the armed services had been working together under difficult circumstances to plan and execute these complex operations.

In preparation for Operation Forager, the assault on the Marianas, Admiral Nimitz assembled a powerful joint force consisting of aircraft carriers, battleships, cruisers, destroyers, amphibious vessels, landing craft and numerous escorts. (4) Operational command was entrusted to Admiral Raymond A. Spruance, Commander of the 5th Fleet.

Task Force 58, a fast carrier group under Vice Admiral Marc A. Mitscher, would provide escort and cover for the amphibious forces. These forces would be commanded by Vice Admiral Richmond K. Turner and consisted of the Northern and the Southern Amphibious Assault Groups. Turner assumed personal command of the Northern Group, which would invade Saipan and Tinian. It included the 2d and 4th Marine Divisions with the Army National Guard's 27th Infantry Division in reserve and the XXIV Corps Artillery in general support (GS).

Once ashore, Marine General Holland Smith would assume command of land operations, grouping all forces under the V Amphibious Corps. The Southern Assault Group, under Rear Admiral Conolly, would invade Guam. Its land component, III Amphibious Corps under Marine Major General Roy S. Geiger, included the 3d Marine Division, the 1st Provisional Marine Brigade, a corps artillery headquarters and the 77th Infantry Division in reserve. (5)

The coming operations clearly demanded joint planning and execution of fires. Initially, naval aviation and gunfire would serve as the primary means of fire support. In addition, units from the Seventh Army Air Forces would strike at long range from the recently captured airstrips in the Marshalls and, later, would be transferred to captured airfields in the Marianas to provide close air support (CAS). Finally, organic and supporting Field Artillery units would provide close and GS fires for the land battles.