Amphibious warfare
The enormous building program quickly gathered momentum. Such a high priority was assigned to the construction of LSTs that the previously laid keel of an aircraft carrier was hastily removed to make room for several LSTs to be built in her place. The keel of the first LST was laid down on 10 June 1942 at Newport News, Va., and the first standardized LSTs were floated out of their building dock in October. Twenty-three were in commission by the end of 1942. Lightly armored, they could steam cross the ocean with a full load on their own power, carrying infantry, tanks and supplies directly onto the beaches. Together with 2,000 other landing craft, the LSTs gave the troops a protected, quick way to make combat landings, beginning in summer 1943.

D-Day: The most famous amphibious assaults of the war, and of all time, were the Normandy landings on 6 June 1944, in which British, Canadian, and US forces landed at Utah, Omaha, Gold, Juno and Sword beaches in the largest amphibious operation in history.
The organizational planning of the landings (Operation Neptune) was in the hands of Admiral Bertram Ramsay. It covered the landing of the troops and their re-supply. Many innovative elements were included in the operation to ensure its success.
Operation Pluto was a scheme developed by Arthur Hartley, chief engineer with the Anglo-Iranian Oil Company, to construct an undersea oil pipeline under the English Channel between England and France to provide logistical support to the landed armies. Allied forces on the European continent required a tremendous amount of fuel. Pipelines were considered necessary to relieve dependence on oil tankers, which could be slowed by bad weather, were susceptible to German submarines, and were also needed in the Pacific War. Geoffrey William Lloyd, the Minister for Petroleum gained the support of Admiral Mountbatten, Chief of Combined Operations for the operation.
Two types of pipeline were developed. The first type was the flexible HAIS pipe with a 3 inch (75 mm) diameter lead core, weighing around 55 long tons per nautical mile (30 t/km), was essentially a development by Siemens Brothers (in conjunction with the National Physical Laboratory) of their existing undersea telegraph cables, and known as HAIS (from Hartley-Anglo-Iranian-Siemens). The second type was a less flexible steel pipe of similar diameter, developed by engineers from the Iraq Petroleum Company and the Burmah Oil Company.

In June 1942 the Post Office cable ship Iris laid lengths of both Siemens' and Henleys' cable in the Clyde. The pipeline was completely successful and PLUTO was formally brought into the plans for the invasion of Europe. The project was deemed "strategically important, tactically adventurous, and, from the industrial point of view, strenuous". After full-scale testing of an 83 km (45 nautical mile) HAIS pipe across the Bristol Channel between Swansea in Wales and Watermouth in North Devon, the first line to France was laid on 12 August 1944, over the 130 km (70 nautical miles) from Shanklin Chine on the Isle of Wight across the English Channel to Cherbourg Naval Base. A further HAIS pipe and two HAMELs followed. As the fighting moved closer to Germany, 17 other lines (11 HAIS and 6 HAMEL) were laid from Dungeness to Ambleteuse in the Pas-de-Calais.
In January 1945, 305 tonnes (300 long tons) of fuel was pumped to France per day, which increased tenfold to 3,048 tonnes (3,000 long tons) per day in March, and eventually to 4,000 tons (almost 1,000,000 Imperial gallons) per day. In total, over 781 000 m3 (equal to a cube with 92 metre long sides or over 172 million imperial gallons) of gasoline had been pumped to the Allied forces in Europe by VE day, providing a critical supply of fuel until a more permanent arrangement was made, although the pipeline remained in operation for some time after.
Portable harbours were also prefabricated as temporary facilities to allow rapid offloading of cargo onto the beaches during the Allied invasion of Normandy. The Dieppe Raid of 1942 had shown that the Allies could not rely on being able to penetrate the Atlantic Wall to capture a port on the north French coast. The problem was that large ocean-going ships of the type needed to transport heavy and bulky cargoes and stores needed sufficient depth of water under their keels, together with dockside cranes, to off-load their cargo and this was not available except at the already heavily defended French harbours. Thus, the Mulberries were created to provide the port facilities necessary to offload the thousands of men and vehicles, and tons of supplies necessary to sustain Operation Overlord and the Battle of Normandy. The harbours were made up of all the elements one would expect of any harbour: breakwater, piers, roadways etc.

At a meeting following the Dieppe Raid, Vice-Admiral John Hughes-Hallett declared that if a port could not be captured, then one should be taken across the Channel. The concept of Mulberry harbours began to take shape when Hughes-Hallett moved to be Naval Chief of Staff to the Overlord planners.
The proposed harbours called for many huge caissons of various sorts to build breakwaters and piers and connecting structures to provide the roadways. The caissons were built at a number of locations, mainly existing ship building facilities or large beaches like Conwy Morfa around the British coast. The works were let out to commercial construction firms including Balfour Beatty, Costain, Nuttall, Henry Boot, Sir Robert McAlpine and Peter Lind & Company, who all still operate today, and Cubitts, Holloway Brothers, Mowlem and Taylor Woodrow, who all have since been absorbed into other businesses that are still operating. On completion they were towed across the English Channel by tugs to the Normandy coast at only 4.3 Knots (8 km/h or 5 mph), built, operated and maintained by the Corps of Royal Engineers, under the guidance of Reginald D. Gwyther, who was appointed CBE for his efforts.
By 9 June, just 3 days after D-Day, two harbours codenamed Mulberry "A" and "B" were constructed at Omaha Beach and Arromanches, respectively. However, a large storm on 19 June destroyed the American harbour at Omaha, leaving only the British harbour still intact but damaged, which included damage to the 'Swiss Roll' which had been deployed as the most western floating roadway had to be taken out of service. The surviving Mulberry "B" came to be known as Port Winston at Arromanches. While the harbour at Omaha was destroyed sooner than expected, Port Winston saw heavy use for 8 months—despite being designed to last only 3 months. In the 10 months after D-Day, it was used to land over 2.5 million men, 500,000 vehicles, and 4 million tonnes of supplies providing much needed reinforcements in France.

Other: Other large amphibious operations in the European theatre of World War II and the war in the Pacific include:
Europe:

Pacific:

Korean War: During the Korean War the U.S. X Corps, consisting of the 1st Marine Division and 7th Infantry Division landed at Inchon. Conceived of and commanded by U.S. General Douglas MacArthur, this landing is considered by many military historians to have been a tactical jewel, one of the most brilliant amphibious maneuvers in history  (See analysis in main article).
The success of this battle eventually resulted in link up with U.S. Army forces that broke out of the Pusan perimeter, and led by the 1st Cavalry Division and its Task Force Lynch, cleared much of South Korea. A second landing by the Tenth Corps on the east coast approached the Chosin Reservoir and hydroelectric plants that powered much of Communist China's heavy industry, and led to intervention by Chinese forces on behalf of North Korea. Amphibious landings also took place during the First Indochina War, notably during Operation Camargue, one of the largest of the conflict.

Suez Crisis and Falklands War: The British Royal Marines made their first post-World War II amphibious assault during the Suez Crisis of 1956 when they successfully landed at Suez on 6 November as part of a joint seaborne/airborne operation code-named MUSKETEER.
Despite all the progress that was seen during World War II, there were still fundamental limitations in the types of coastline that were suitable for assault. Beaches had to be relatively free of obstacles, and have the right tidal conditions and the correct slope. However, the development of the helicopter fundamentally changed the equation.
The first use of helicopters in an amphibious assault came during the Anglo-French-Israeli invasion of Egypt in 1956 (the Suez War). Two British light fleet carriers were pressed into service to carry helicopters, and a battalion-sized airborne assault was made. Two of the other carriers involved, HMS Bulwark (R08) and HMS Albion, were converted in the late 1950s into dedicated "commando carriers."