USS Arlington (LPD 24) is the culmination of a century of attempts to answer one question: how do you move heavy equipment from the sea onto a beach without piers or other port facilities? That is the central problem of amphibious operations, whether or not the enemy is waiting on the beach to shoot back. Whoever lands from the sea has to build up enough strength quickly enough to fight effectively, and that must include armor and artillery and also supporting vehicles.
How do you move heavy equipment from the sea onto a beach without piers or other port facilities?
For the United States, attempts to solve the problem go back to before World War I, when the Navy was being designed for what must now seem an odd scenario: defense of the Monroe Doctrine against a European (for which read German) incursion. The U.S. fleet would have to rush south, creating a temporary base from which it could engage the enemy fleet. The Marines would have to defend that base with, among other things, artillery. It had to be landed from the sea, mostly over an unimproved beach. The Navy turned to standard merchant ship practice: ships often unloaded by crane into lighters (flat-bottomed barges), which ferried things to the beach. Thus the first U.S. special-purpose Marine Corps transport, USS Henderson, was designed to carry special artillery lighters that could beach and unload using ramps.
By the time the ship was completed, the United States was fighting in World War I, and it was a lot more important to transport troops to ports in France than to seize and equip temporary bases. However, when the Navy and the Marines turned to the problem of seizing Pacific islands in a possible war against Japan, they faced much the same problem for which USS Henderson had been conceived, and they chose much the same solution. It was generally assumed that the technical problem was how to get from ship to beach, the solutions including the famous 36-foot Higgins boat (the LCVP), which features in so many World War II movies. It is the boat that runs up onto the beach, packed with soldiers (who have not exactly enjoyed the rough ride from the ship). Once it beaches, its somewhat protected ramp slams down onto the beach, and the troops run ashore. Larger versions carried vehicles. All of these boats differed from the ones envisaged before World War I in that they had to deal with surf. That required sophisticated hull design. The pre-1914 artillery lighters were intended to land in a sheltered area, because by definition that was the sort of harbor the Navy would have chosen as a temporary fleet base.
Using small boats simplified transport design. The only important differences between, say, an attack transport and a cargo liner of current type were that the attack transport carried davits for more small boats and that its accommodation was far more spartan than that in the merchant ship – in war-built transports troops lived in the holds, in bunks up to seven tiers high. The cranes that loaded cargo from ship to boats were much the same as those which unloaded commercial ships at docks, or into lighters in a roadstead. These similarities explain how the Navy managed to convert merchant ships into attack transports in days or weeks in 1940-41. The only really novel items were the surf-capable beaching boats.
After being forced out of Europe in 1940, the British thought long and hard about how to get back. They became convinced that any landing force had to bring masses of armor with it.
The rub was that whatever or whoever was going ashore first had to get into those small boats. It was simple enough to launch the boats themselves. If they were small enough, they could be lowered from davits, like lifeboats. If they were larger, they could be lowered into the water by crane. Loading them, either with troops or with vehicles, was another thing. Even near a beach, a ship would roll and pitch. Small unloaded boats would be far livelier. Troops could scramble down cargo nets, but lowering a vehicle of any kind into a rolling, pitching boat was like threading a moving needle. It could certainly be done, but not very quickly. Unfortunately, speed was vital. The force on the beach had to be built up quickly enough to deal with enemy counterattack. The unloading ships were lucrative targets, best unloaded quickly before they could be attacked. In Pacific landings, for example, every effort was made to get transports away from the beach by nightfall, when Japanese night bombers were expected to attack. If the transports were not completely unloaded by the time they had to leave, the troops already ashore might suffer badly – as at Guadalcanal.
The solution came from the British. Like the U.S. Navy, the Royal Navy spent time between wars thinking about amphibious operations. It had conducted the first modern amphibious operation at Gallipoli in 1915. Although that operation was later widely considered a failure, that does not seem to have been the British view at the time. The British drew the lesson instead that although the landing succeeded, the force had not built up quickly enough to overmatch the corresponding Turkish buildup. Had the British force moved inland more quickly, or had it been stronger earlier, the Turks would have been defeated.
Encouraged by Gallipoli, the British planned and prepared for a division-size landing in Flanders in 1917. The lesson they drew from Gallipoli was that more power had to be landed more quickly. One proposal was to land tanks from beached ships using ramps. Incidentally, the U.S. Marines shared the British view, which is why they espoused amphibious assault in the 1930s.
The great difference between British and U.S. views on amphibious assault was that the British were interested in landings on broad shores. They assumed that an astute commander could always find a relatively undefended landing place. The Marines had no such choice, since they planned to attack small islands that could be completely fortified – as proved the case in the Pacific. The difference mattered, because British thinking enormously affected wartime operations in European waters. In many cases it was indeed possible to land unopposed, the issue being whether the enemy could build up more rapidly than the attacking force (as at Gallipoli). The point of the deception campaign leading up to Normandy was to limit German fortification there, and also to keep the Germans from building up the force nearby (the bombing campaign against French railroads helped enormously). The hope to achieve surprise also explains the dawn landing (in the Pacific, the Navy landed during the day) and the lack of pre-assault bombardment, which proved unfortunate.
After being forced out of Europe in 1940, the British thought long and hard about how to get back. They became convinced that any landing force had to bring masses of armor with it. Their idea of surprise made it impossible to use an existing port (in Normandy the U.S. and Britain created an artificial port, but only after the beach had been secured). The key question would be how rapidly armor could be built up on a beachhead. The first approach was much the same as imagined in 1917: build or convert a conventional ship which could beach carrying tanks. The tanks could drive down a ramp. The British actually converted some shallow-draft tankers, and they ordered some specially-built ships. They realized that they lacked the resources to build enough such ships, so by early 1941 they were hoping to buy them in North America. Once Congress had passed the Lend-Lease Act in March 1941, that became a practical proposition.