In the early 1920s, U.S. military strategists began planning for numerous wartime contingencies, focusing primarily on Japan, the nation's Pacific rival. Recognizing the navy's need to secure advance operating bases on islands west of Hawaii in any war against Japan, the Marine Corps adopted amphibious assault as its raison d'être.
Integrating the newly constituted Fleet Marine Force into the U.S. Navy, the Marines streamlined their bureaucracy and concentrated on preparations for seizing and defending advance bases in the Pacific. The corps assigned personnel to naval intelligence and planning staffs and began educating its officers in the tactics of amphibious operations. Lieutenant Colonel Earl "Pete" Ellis's exhaustive studies of Japanese-held Pacific islands in the early 1920s formed the nucleus of the Marines' amphibious assault doctrine. In 1934, the corps published a more exhaustive guide to amphibious operations, The Tentative Manual for Landing Operations, and held a series of fleet landing exercises designed to test its concepts. These exercises were crucial in highlighting the need for detailed logistical planning, speed in ship-to-shore movement, overwhelming fire superiority from air and naval bombardment, and specialized equipment to successfully carry out opposed landings. Although Marine aviation utilized previous experience in Latin America to develop rudimentary close-air support tactics based on dive-bombing (which the German Luftwaffe then adopted), the navy's ambivalence toward developing close-in naval gunfire support techniques and constraints on the procurement of new equipment severely limited the development of U.S. amphibious warfare prior to 1939.
Between 1939 and 1941, as the U.S. military buildup went forward, the Marine Corps tripled in size from some 25,000 to 75,000 men and improved its amphibious capabilities. However, the corps was spread thinly to cover a wide range of duties in garrisons and aboard ships, from Iceland to the Caribbean to Hawaii and numerous smaller islands throughout the Pacific.
On 7 December 1941, Marines aboard battleships at Pearl Harbor and at nearby airfields assisted in defending Hawaii against the Japanese attacks. Elsewhere in the Pacific, isolated Marine garrisons on Guam and in China had little choice but to surrender. Marines on Wake Island and in the Philippines valiantly attempted to resist Japanese invasions, but Wake fell after two weeks of resistance, and the Philippines surrendered in May 1942.
Marines were at the forefront of early U.S. operations against Japan. In the southwest Pacific, the 1st Marine Division carried out assaults in the Solomon Islands in August 1942. The long campaign for Guadalcanal revealed the complexities of conducting amphibious operations under battle conditions, including the need for increased logistical support and a simplified command-and-control structure. Advancing up the Solomons from 1942 to 1944 toward the Japanese fortress at Rabaul, the Marines found themselves engaged in jungle warfare against a determined Japanese foe.
In 1943, encouraged by success in the Solomons, the U.S. Navy and Marine Corps undertook a thrust through the Central Pacific toward the main Japanese islands. The atolls of the Gilbert and Marshall Islands proved a different kind of challenge to the Marines than the jungle warfare of the southwest Pacific. Ineffective fire support, confused communications, and a shortage of proper equipment made the initial assault at Tarawa a bloody and sobering affair.
Employing the lessons learned from Tarawa to refine their amphibious doctrine, the Marines advanced through the key Marshall Islands atolls of Kwajalein, Roi-Namur, and Eniwetok. During the summer of 1944, Marines landed on Saipan, Tinian, and Guam in the Marianas. They also learned how to conduct sustained combat operations on these larger, extensively fortified islands. In the fall of 1944, Marine infantry and aviation forces assisted General Douglas MacArthur's advance on the Philippines. Marines landed on Peleliu in September and suffered heavy casualties in a savage, week-long battle. From September 1944 to April 1945, Marine Corps tactical air support became a vital component of army operations on Leyte and Luzon.
In February 1945, the Marines invaded the island of Iwo Jima in their most spectacular and costly operation of the war. Nearly the entire 21,000-man Japanese garrison died defending the island, while inflicting almost 30,000 casualties on American forces in a 36-day slugfest. During the battle, a journalist snapped a photo of five Marines and one navy corpsman raising a flag on Iwo's Mount Suribachi. This image instantly became an icon of Marine Corps valor and esprit de corps as well as a symbol of American fortitude in World War II. In June 1945, the Marines and the army secured Okinawa, just 360 miles from Japan, after three months of ferocious combat in the hills and caves across the island. After the Japanese surrender on August 1945, the Marines served throughout the Pacific in occupation duties.
World War II was a defining moment for the Marines. Their seemingly prophetic development of amphibious assault doctrine in the interwar period proved invaluable to winning the Pacific campaigns, and their prior planning and experience also aided the army-led invasions of Europe. The corps had grown to twenty times its prewar strength, with approximately 500,000 men in six Marine infantry divisions and four Marine air wings. It had honed its amphibious doctrine, while expanding its aviation and combat support capabilities. Though the corps comprised less than 5 percent of the U.S. military in the war, Marines constituted nearly 10 percent of all American wartime casualties, with 19,733 killed and 67,207 wounded.
Despite continued and often heated interservice clashes between the army, the navy, and the new U.S. Air Force, the Marines' combat performance during World War II further attached the corps to the public, thus ensuring the service would survive demobilization as a separate institution within the navy and an elite component of the U.S. military establishment.
Derek W. Frisby
Alexander, Joseph. A Fellowship of Valor: The Battle History of the United States Marines. New York: Harper Collins, 1997.; Frank, Benis M., George W. Garand, Frank O. Hough, Douglas T. Kane, Verle E. Ludwig, Bernard C. Nalty, Henry I. Shaw Jr., Truman R. Stroubridge, and Edwin T. Turnbladh. History of U.S. Marine Corps Operations in World War II. 5 vols. Washington, DC: Historical Branch, Headquarters, Marine Corps, 1958–1968.; Millett, Allan R. "Semper Fidelis": A History of the United States Marine Corps. Rev. ed. New York: Free Press, 1991.; Moskin, J. Robert. The U.S. Marine Corps Story. Rev. ed. New York: McGraw-Hill, 1987.