By mid-1943, a glut of newly built ships and aircraft was arriving in the Pacific, churned out by American shipyards and factories fully converted to wartime production. It was not only the volume of weapons and machinery that added to American might, but their modernity as well. Naval aircraft, for example, such as the Hellcat fighter plane, were speedier, more maneuverable, and far more lethal than their predecessors.

Tens of thousands of soldiers and Marines were also arriving, divided between the two theater commanders, General Douglas MacArthur, based in Australia, and Admiral Chester Nimitz, headquartered at Pearl Harbor. Both would have to wrestle away key outposts from the Japanese, whose ranks were filled with zealous fighters clinging to an ancient warrior code and vowing a fight to the death.

As MacArthur embarked on an offensive in New Guinea—a precursor to his long-planned return to the Philippines—Nimitz plotted his next moves in the South and Central Pacific, aiming to use those islands as steppingstones to Japan. In the path of both MacArthur and Nimitz was the great Japanese naval and air base at Rabaul, defended by a garrison of 100,000 troops. To avoid a costly and time-consuming fight, the base was simply bypassed, cutting it off from reinforcement and re-supply. In the months ahead, other outposts would be similarly leapfrogged, and the “island hopping” strategy paid clear dividends, allowing US forces to avoid bruising battles and hasten their westward advance.

Some strongholds, however, had to be taken, as anchorages and airstrips were needed along the path to Japan. In November 1943, the 2^nd Marine Division made an amphibious landing on Tarawa, a tiny atoll in the Gilbert Islands planners eyed as a future air base. Nearly 5,000 crack Japanese troops were entrenched behind the beaches, and as the Marines scrambled out of their amphibious tractors (amtracs), they were met with a hailstorm of enemy gunfire. A second wave of Marines was sent in, but the tides had receded, preventing the amtracs from scaling the coral reef surrounding the island. As the Marines abandoned the boats and waded ashore, scores were cut down in the surf by Japanese machine-gun and sniper fire. The Marines finally managed to inch off the beaches, but it took three days to subdue the garrison on Tarawa, and the result was a bloodbath for both sides. All but seventeen defenders were killed, with the Marines suffering more than 1,100 dead.

Seven months later, another fierce contest unfolded on Saipan in the coveted Marianas Islands. The heavily defended island had a substantial civilian population, and though it was 3,500 miles from Pearl Harbor, it was barely a third of that from Japan. It became another bitter struggle, with US casualties topping 16,000 and more than 24,000 Japanese killed. An estimated 22,000 civilians also died, with many taking their own lives, convinced by Japanese propaganda that the invading Americans were monstrous demons.

With the capture of Saipan and its airfields, Japanese cities were within range of new B-29 Superfortress bombers. Though it was hoped a sustained bombing campaign of the home islands would compel the Japanese to surrender, planners still anticipated an eventual invasion of Japan itself. That required Nimitz and MacArthur to continue their respective drives across the Pacific, where more harrowing campaigns loomed.