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The development of American amphibious doctrine was an outgrowth of the great energy and momentum built up during the expansion of the United States near the end of the nineteenth century. With the Spanish-American War, the Americans moved from their continent and into the reaches of the Pacific with its expansion to Hawaii, Guam, Samoa and the Philippine Islands. This expansion required a navy to protect the new possessions and with the threat of the Japanese Empire for motivation, Washington allocated the funds needed to increase the size of the navy. The navy required forward bases in order to sustain its fleets. The need for the acquisition and security of these new bases required forces capable of offensive and defensive action. In an extensive memorandum, Major Pete Ellis U.S.M.C. outlined the operational problem in 1921: “In order to impose our will upon the Japanese, it will be necessary for us to project our fleet and land forces across the Pacific and wage war in Japanese waters. To effect this requires that we have sufficient bases to support the fleet, both during its projections and afterwards. As the matter stands at present, we cannot count upon the use of any bases west of Hawaii except those which we may seize from the enemy after the opening of hostilities.” Ellis accurately predicted the need to seize, secure and occupy islands held by the Japanese. The terrain required forces capable of deploying from ships, advancing inland and securing the gains. The Marine Corps assumed this mission and set to work developing the operational and tactical doctrine required. It would by unwise to assume that the Navy and Marines had a workable doctrine by the start of World War Two, funds were short in the inter-war years and the development moved forward in fits and starts. But by the start of WWII, the United States and an untested offensive amphibious doctrine.

The Army officially adopted the Marine-Navy amphibious doctrine, but for the most part, did not make use of it. In the North African and Mediterranean, British doctrine was used. The thinking, makeup, conditions and practices of the army were sufficiently different from those of the navy/marines team to prevent adoption of the navy-centered doctrine, and the influence of the British in 1942/1943 on the conduct of operations all of which were combined arms, was decisive. It was the feeling in the army that the navy/marine doctrine was better suited for the small scale operations against atolls and islands in the Pacific than to the “mighty endeavors” the army faced.

In 1941, the War Department published U.S. Army FM 31-5, “Landing Operations on Hostile Shores“, which stated: “This manual is based to a large extent on Landing Operations Doctrine, U.S. Navy 1938.” The navy’s document, in turn was based on the Marine Corps FTP 167 “The Tentative Manual for Landing Operations“. These two documents, FM 31-5 and FTP 167 were refined steadily throughout the war, but remained the basic guides for both planning and training of all U.S. amphibious operations during World War Two.

The chief of staff of the 1st Infantry Division, Colonel Stanhope Mason, one of the most experienced army officers in the ETO in amphibious operations stated; “The Navy’s manual (FTP167) went no further than maximum loading of life boats. This was a pure transportation problem that took absolutely no heed of the necessity for ground units to maintain their unit integrity once landed on the beach where they would have to fight.” The 1st Infantry Division conducted more amphibious operations in the ETO than any other division. Mason recognized that the doctrine formulated by the navy was incomplete and inadequate for the 1st Infantry’s needs. What he did not recognize was the influence exerted by the British at the operational level.

The doctrinal thinking of the Marine Corps differed from that of the British: Night landings, except possibly for small reconnaissance parties going ashore prior to the main attack, were discouraged as too dangerous. Transports carrying the assault troops should approach the transport area under the cover of darkness, but the landing should ordinarily be made during the early morning so as to permit the fullest use of all weapons and to afford the landing force ample daylight in which to secure the beachhead. Naval vessels should take position on the flaks of the landing troops and sweep the beaches during the ship-to-shore movement. Aircraft should be employed in full measure not only for reconnaissance but also for strafing after the troops were landed.

Marine Corps operations were heavily dependent on naval gunfire support; surprise played no part. This thinking, however, never developed in the European Theater of Operations. The British simply lacked the resources to conduct warfare with firepower and their tradition of amphibious raids dominated their thinking. The marines preferred early-morning landings in order to maximize the hours of daylight needed to establish the beachhead, with assistance from air and sea forces. British operations involved more phases, and each phase had to be executed sequentially. British operations were more intricate and because of the environment, conditions and circumstances varied considerably in each landing, combined Mediterranean and European operations required far more detailed planning than did Pacific operations. British doctrine also required more detailed intelligence on the enemy’s situation and terrain than did Pacific doctrine. In the Pacific, it was the Navy’s responsibility to cut off the islands from all outside assistance. This was not possible on the continent. Thus, the need to identify all forces that could influence the situation in a given area and the quality and capacity of all major transportation arteries became a prime requirement for amphibious landings.

The American practice of war at the strategic and operational levels was not to attack the enemy’s weakness, but to attack its strengths, to seek out the enemy’s main army and destroy it. This is the so-called “direct approach.” U.S. amphibious doctrine this stressed daylight assaults, which would allow the maximum possible use of strategic/operational resources.

As FM 31-5 states, “Naval gunfire and combat aviation must be concentrated in support of the landing. Even a relatively small number of enemy machine guns and light artillery pieces firing under favorable conditions have a devastating effect on units as the approach and land on the beach. Assault units will probably be unable to get ashore and advance against this fire unless adequately supported by ship fire and combat aviation.”

The landings at Gallipoli, North Africa, Sicily, Salereno all proved the deadly accuracy of this. With each invasion, the need for preinvasion bombardment and bombing increased.