In world war ii the amphibious attack was uniformly successful. If we make exceptions of Dieppe, which was a raid, and the Jap failure at Milne Bay, a small operation, it is possible to make this generalization. The Jap failure at Midway was not an amphibious failure but a naval one, since the expedition never entered the amphibious phase. What caused the amphibious assault, whether Japanese, British, or American, to be so uniformly successful? Principally, I think, because two basic principles of war were adhered to, Concentration of Force and Surprise. Landings were not attempted unless it appeared that at least local command of the sea and a measure of air superiority could be achieved and maintained in the assault area. In Europe throughout and in the Pacific during the early stages of the war, the greatest efforts were made to preserve surprise until D day.
Surprise Subordinated
In the latter part of the war in the western Pacific surprise was deliberately subordinated, in several instances, to concentration of force, by employing strong naval forces to isolate the objective—usually an island— and give it a merciless pounding for several days prior to D day. The factors which made this course practicable were: (a) control of the sea and air over a wide ocean area surrounding an island target, (b) the consequent capability of sealing off the objective so that the defender could not reinforce his garrison after it became apparent to him that he was going to suffer amphibious attack, and (c) the abundance of fire support ships and naval aircraft which could be allotted to such a preliminary softening up phase without dislocating the purely naval commitments of the Pacific Fleet.
These factors did not obtain in the early days of our Pacific offensive. Guadalcanal was not attacked in this way. But, as the War continued, this method became increasingly feasible as our superiority at sea and in the air became almost complete through the destruction of Japanese naval and air power in the sea engagements of Midway, the Philippine Sea, and Leyte Gulf, and through our greater naval building potential.
This method was not used in the European Theatre by American forces and never used anywhere by the British. We could not have employed this method in the European landings because two of the factors were never present: control of a wide ocean area surrounding an island target and the capability of sealing off the target from reinforcement. The British never at any time considered this method because of the third factor. They never had fire support ships available in sufficiently lavish numbers to implement this method.
Two District Types
The basic difference between Pacific amphibious warfare and European amphibious warfare is a simple and obvious one. In Europe the landing assault was only a means. It was the necessary prerequisite to the invasion of a land mass entirely in enemy or neutral hands, the establishing of a reentrant on an enemy held continent without which our land forces could not come to grips with the enemy to defeat him.
In the Pacific the amphibious assault was much more an end in itself. In many cases the landing force, that is, the assaulting amphibious divisions, had the mission not only of establishing a beachhead but of defeating the enemy garrison and capturing the entire objective. In Europe amphibious warfare was characterized by the attack of continental land masses with short sea communications supported by land based aircraft. In the Pacific it was much more the island seizure type of operation with long sea communications which necessitated carrier borne tactical air support.
The emphasis placed on various aspects of the amphibious problem in these two distinct types of assault differs markedly. The long range island seizure is predominantly a naval operation. Although its object may well be to establish a base for the Air Force, or simply to deny it to the enemy, the whole operation is primarily naval in character. The landing force, be it marines or army, is in a subordinate, though essential, role. The object of the operation is not so much the defeat of the enemy garrison, whatever its size, though this is a sine qua non, but the occupation of the island in order to establish base facilities for supplying and supporting our fighting forces closer to the source of enemy power.
The attack of a continental land mass is something else again. First of all, it is not predominantly a naval operation but a military one, though it is scarcely necessary to observe that you cannot lay on an amphibious operation without the Navy. The naval effort, however, is really but a means to project vast land forces ashore for the prosecution of a land campaign. Its role is not dissimilar to the role of the Air Force in delivering airborne troops to their objective and providing the accompanying tactical air support and airborne re-supply.
In this type of operation the assaulting forces, the amphibious divisions, have a limited objective—the establishment of a beachhead or a lodgement area into which we will then pour more infantry and armored divisions, develop logistical support facilities, and establish air strips in order to break out and defeat the enemy’s ground forces. The emphasis here is not so much on the success of the initial assault. Though it may prove to be a hard fight, its success must be pre-supposed. The emphasis is much more on winning of the build-up race, that crucial ten days to two weeks from D day during which we are pouring men and material into the beachhead in order to achieve a sufficiently large and balanced force to begin the land campaign before the enemy can contain us by moving up his general reserve.
In this type of operation—Normandy is the classic example—it is difficult to delineate sharply the division between the assault and establishment of the beachhead and the subsequent land campaign in a logistical sense, though tactically the phases are clear and distinct. The former is a necessary prelude to, and a part of, the latter. It is the first phase, but the land campaign develops from it with scarcely a pause. The operation gradually sheds its amphibious character until the full pattern of continental warfare develops.
Here we find the principle of surprise looming large in the minds of the planners. There are grave objections to battering the beaches with naval gunfire for days prior to the assault. The air can systematically bombard the assault area beforehand without jeopardizing surprise because the assault area can be only a small part of a much larger area which is subjected to intensive aerial bombardment. To employ naval gunfire effectively, however, it is necessary to concentrate considerable naval strength in the immediate area of the assault. If this is done prior to D day, it may give the whole show away. This means that the enemy could begin to move his general reserve, thus confronting us with a stronger defence in the assault area than our planners had anticipated. This would not only jeopardize the success of the initial assault but also the all important build-up race.
The Invasion of Japan
Operation “Olympic,” the invasion of Japan, was to have resembled the island seizure technique rather than the Normandy landing. The D day assault would have been on a much larger scale than the Normandy landing. Surprise was to have been almost completely subordinated to concentration of force. The Pacific Fleet was to have pounded away at the assault areas for days on end. All mineable waters were to have been swept. “Olympic” (without benefit of atom bomb) would unquestionably have been successful. It may be claimed that the home islands of Japan are sufficiently large, comprising as they do the entire enemy country, to be considered a land mass. Would it have been correct therefore to have employed this method to invade Japan rather than the Normandy pattern? Conversely could Europe have been successfully attacked in this way?
My answer to the first question is yes; to the second, no. You may call Japan a land mass, but it is not a continental land mass. Let us apply the three factors to the situation. We enjoyed almost absolute control of an ocean area surrounding an island target. We were able to seal off the target so that the enemy could not move any of his best and unbeaten ground forces in China back to augment the metropolitan defense forces when invasion threatened. We had the necessary sea and air forces to do the job. Thus the three factors which must be present to make this method practicable prevailed.
But, it may be asked, what about the considerable forces deployed in Japan for the defense of the home islands? Were they not sufficiently large to constitute a threat to the landings on the southern island of Kyushu? If we planned to almost ignore surprise and operate huge naval forces off the areas chosen for assault for many days prior to D day, how could we have prevented the enemy from concentrating his strength in the threatened areas? Yes, the enemy could certainly have endangered the success of the assault if he could have concentrated his forces to oppose us on Kyushu. He would not have been able to do so, however. Our air strength would have been able to prevent him from doing so because of the geography of the island and a peculiarity of Japanese communications. Kyushu is mountainous. There are many defiles. Road transport was secondary to rail communications in importance. Our air power would have been able to effectively seal off the assault areas from enemy reinforcement by disrupting rail communications.
It is obvious that Normandy could not have been attacked in this way under the conditions prevailing at the time. But let us keep an open mind. It is possible that air power in the future will be able to effectively isolate a part of a continental land mass in the same way that sea and air power were able to isolate an island during World War II.
Conclusions
So the post-war amphibious planners are heir to two different concepts of large scale amphibious operations. If we ever have to mount one of such proportions again what will the pattern be, “Overlord5’ or “Olympic”? I believe it will depend entirely on the degree of superiority at sea and in the air, or rather the degree of superiority which we can expect to achieve and maintain, at the time and place of landing. If we have to attack a still strong and vigorous enemy who is prepared to defend his coast line, if he has good road communications to the hinterland, if he still has a measure of air strength left with which to oppose our own air forces, then we shall have to preserve surprise, and it will be the Normandy pattern. If, however, the enemy is off balance, if his war potential is greatly reduced, his communications badly disrupted, and our own air forces roam the skies unopposed—then it will be the Pacific pattern. If such favorable conditions prevail, then a continental land mass can be assaulted in the same manner as Iwo Jima, provided air power can isolate the area chosen for the assault as effectively as naval and air power could isolate Iwo Jima in 1945. We then, in effect, hurl the trinity of our land, sea, and air power at only the local defending enemy ground forces.
As to whether a large scale landing will ever again be undertaken against an enemy who is still able to defend his coast line with vigor, I shall not venture an opinion. It is difficult to relate the large scale amphibious operation logically to the period of a war between two great powers when the atom bomb and other weapons of mass destruction are being used by both sides. It will more likely occur after the atomic phase is won. It would then resemble much more the occupation of Japan in 1945, a landing unopposed, rather than “Overlord” or “Olympic.”