The United States entered World War II 27 months after it began officially with Adolf Hitler’s invasion of Poland in September 1939. It took a direct Japanese attack on Dec. 7, 1941, and a German declaration of war four days later to get us fully engaged. While we slept, Hitler extended his dominion over most of Europe and invaded Russia, with excellent prospects for success. In the east, Japan extended her empire to Manchuria, eastern China, Indo-China, Burma, the Malay Peninsula and Singapore, the Philippines, the Dutch East Indies, and Thailand. Italy, the third Axis power, proved more of a burden than a help to her allies. Germany and Japan alone, however, were powerful enough to create a new totalitarian order in the world. But they had to move quickly, before the United States became aroused, since neither had the industrial capacity to defeat us. Fortunately, their hubris blinded them to this fundamental reality, and they awakened the sleeping giant in the nick of time.

Once in the war, the United States became the leader of a tripartite alliance with the British and Russian empires − a strange coalition that Hitler, until the very end, thought would fall apart. The first job of the Allies was to stop German and Japanese advances. This happened quicker than anyone expected. The Nazi invasion of Russia in 1941 failed to reach Leningrad, Moscow, or the Caucasus before the onset of winter, and once the fighting resumed in May 1942, Hitler was defeated at Stalingrad in a few months. Japanese expansion was halted even sooner − at the Battle of the Coral Sea the first week of May 1942, and a month later at the Battle of Midway.

Having stopped the Axis advances, the Allies then had to roll them back − a daunting task. The United States was required to mount expeditionary assaults in the Atlantic, the Mediterranean, and the Pacific on a scale never before imagined. Misguided disarmament policies after World War I had left us militarily unprepared, forcing our armed forces to pay dearly while we got fully geared up to fight. By the middle of 1943, however, America’s industrial strength was totally engaged, and our superb political and military leadership, supported by the indomitable patriotism of our fighting men and women, doomed our enemies.

Even though ultimate victory was never in doubt, the Axis fought with a tenacity that tried our soul. Germany’s relative strength led Roosevelt and Churchill in 1941 to give the European Theater priority, but because of Pearl Harbor, America was not about to ignore the Pacific. Thus, we fought a gigantic, two-ocean war simultaneously, carrying nearly the entire burden against Japan.

America’s Army chief, Gen. George Marshall, recommended a cross-channel invasion in 1942 aimed directly at the heart of Germany, taking advantage of Hitler’s preoccupation with Russia. Churchill and Roosevelt, however, decided they were not yet ready and opted instead for a landing in North Africa in November 1942.

With Hitler still distracted in Russia, a combined American-British expeditionary force under Gen. Dwight D. Eisenhower made a remarkable crossing of the Atlantic, avoiding German U-boats, and began landing in Morocco and Algeria on Nov. 8, 1942. Because Vichy Adm. Jean-Francois Darlan decided to change sides, the Allied landings at Oran, Algiers, and Casablanca met minimal resistance. Eisenhower pressed on toward Tunis to meet British Gen. Bernard Montgomery’s Eighth Army − fresh from its triumph at Alamein in early September. They planned to trap German Gen. Erwin Rommel in Tunis, thus reclaiming all of North Africa. Hitler, however, despite being bogged down in Russia, reinforced Rommel, igniting a long battle that did not end until May 13, 1943.

Even before Eisenhower’s landing, an American expeditionary force on Aug. 7, 1942, landed on Guadalcanal, one of the Solomon Islands in the southwestern Pacific, to start rolling back Japanese conquests. Only 2,200 Japanese guarded the island and its unfinished airbase, making the initial amphibious landing relatively easy for the U.S. Marines. But the Japanese high command, realizing this was just the beginning, made a mighty effort to defeat us. As Tokyo committed more resources, the fighting turned grim, lasting until Feb. 7, 1943. Sixteen hundred American Marines and soldiers died and 4,200 were wounded, while 23,000 Japanese soldiers were killed. Five major naval battles were fought, in which a combined total of 24 warships were sunk. The number of sailors and airmen lost was heavy.

In every theater, amphibious landings were the hallmarks of American expeditionary warfare, as we became highly proficient at combining, in the words of Samuel Eliot Morison, “air, surface, submarine, and ground forces to project fighting power irresistibly across the ocean.” Learning and improving as we went along, we nonetheless paid a heavy price in blood for not being prepared earlier.

By the summer of 1943, American industry was producing weapons in stupendous quantities. “The United States Navy … enjoyed almost an embarrassment of riches,” wrote British historian John Keegan. Large, Essex-class carriers; light, Independence-class carriers; escort carriers; new battleships; refurbished old battleships; heavy and light cruisers; dozens of new destroyers; new, fast transports; cargo vessels; and large numbers of specialized support ships were all being built.

To make our fleets even more devastating, we developed the capacity to operate them at long distances from their bases for extended periods. Utilizing specially designed ships for fuel, repair, ammunition, spare parts, and other supplies, medical services, and even floating dry docks, American expeditionary forces, particularly our fast carriers, could operate at heretofore unheard of distances from their home bases for a long time. In addition, the supply forces allowed us to set up advanced bases rapidly and to re-supply them quickly.

We developed nine different landing and beach craft – LSTs (Landing Ship, Tank), LVTs (Landing Vehicle, Tracked−amphtracs) LCMs (Landing Ship, Mechanized−tank loaded), LSDs (Landing Ship, Dock), LCPs (Landing Ship, Personnel), LCIs (Landing Ship, Infantry), LCTs (Landing Craft, Tank), LCVPs (Landing Craft, Vehicles and Personnel), and LSMs (Landing Ship, Medium), as well as the amphibious truck, DUKW. American factories produced in excess of 80,000 of these indispensable vehicles. They played essential roles in the amphibious landings at Sicily, Salerno, Anzio, Southern France, Normandy, and against the Japanese on New Guinea, the Solomons, the Philippines, the Gilbert, Marshall, Caroline, and Mariana Islands, and on Okinawa.