The Aleutian Islands are known for their rugged, treeless tundra and almost perpetually foul weather, but during the early days of World War II, they were considered a valuable piece of real estate. Fresh off their success at Pearl Harbor, the Japanese were looking to consolidate their gains in the Pacific while also stymying any potential U.S. attacks against their home islands. The Aleutians—situated at the center of the shortest route between the United States and Japan—were viewed as a key part of their defensive shield. The Japanese high command scheduled an advance on the islands for June 1942. While the bulk of their navy looked to demolish the American Pacific fleet at the Battle of Midway, a smaller force consisting of two aircraft carriers and a handful of destroyers, cruisers and submarines sailed for the frozen north.

Damage to Dutch Harbor after the Japanese raid.

The Alaskan campaign kicked off on June 3, 1942, when 17 Japanese aircraft carried out a bombing raid on Dutch Harbor, the largest American Army and Navy installation in the Aleutians. The attack was hampered by heavy fog—a few planes became lost and never reached their target—but a swarm of Japanese bombers and Zeroes returned the following day and destroyed the base’s oil storage tanks and part of its hospital. Having struck an early blow, the Japanese looked to establish their first foothold in North America. On June 6 and 7, 1942, they landed some 2,500 troops on Kiska and Attu, a pair of windswept islands on the western end of the Aleutians.

Japan’s land grab in the Aleutians marked the first time an enemy had invaded U.S. soil since the War of 1812, and it provoked both fear and outrage among American military brass. Not only did the Japanese garrisons threaten U.S. and Soviet shipping, there were concerns that Kiska and Attu might be used as staging grounds for attacks on the Alaskan mainland or the Pacific Northwest. The first efforts to oust the occupiers commenced that summer. In August, U.S. forces landed unopposed on Adak, an Aleutian outcrop some 200 miles away from Kiska. After constructing an airfield in the span of just two weeks, they began regular bombing runs over Kiska and Attu.

U.S. troops carrying a stretcher on Attu.

The Aleutian campaign devolved into a standoff during the winter of 1942-43, in part because of the brutal Alaskan winter. The rain, rough seas and soupy fog of the North Pacific made it difficult for aircraft to fly safely, and ground troops were subjected to extreme winds and bone-chilling cold. When U.S. forces claimed the island of Amchitka in January 1943, they were immediately hit by a “williwaw,” a type of fierce Alaskan squall that crushed or grounded several of their ships. Even on relatively mild days, conditions were often deplorable. “There was a gauge to measure the wind,” wrote detective novelist Dashiell Hammett, who served as a U.S. Army corporal in the Aleutians, “but it only measured up to 110 miles an hour, and that was not always enough.”

Despite the bitter weather, U.S. forces closed in on Attu and Kiska in early 1943 and set up a naval blockade around the islands. A three-hour battleship duel erupted when the Japanese tried to run the blockade in late March, but the smaller U.S. fleet managed to fight them off and win control of the sealanes. As spring approached, Navy Rear Admiral Thomas Kinkaid finally unveiled a plan to sweep the now-isolated Japanese occupiers from the Aleutians. Dubbed “Operation Landcrab,” the scheme called for U.S. forces to stage an amphibious attack on 15-mile-wide Attu, the more lightly defended of the Japanese-held islands. If successful, the Americans would have Kiska surrounded.

U.S. Navy Rear Admiral Thomas C. Kinkaid. (Credit: Dmitri Kessel/The LIFE Picture Collection/Getty Images)

Following an extended bombing campaign, Operation Landcrab commenced on May 11, 1943. In what amounted to the Army’s first major amphibious invasion of the war, over 12,000 troops stormed beaches on both the northern and southern portions of Attu. The landings were greeted only by an ominous stillness. Unbeknownst to the Americans, Japanese Colonel Yasuyo Yamasaki had ordered Attu’s 2,500 defenders to fall back to a maze of foxholes and trenches in the island’s mountainous interior. It was only when the G.I.s tried to advance inland that his soldiers finally opened fire.

For the next several days, the American soldiers slogged across Attu’s boggy terrain, battling the Japanese in mountain passes and on barren hilltops. The U.S. force boasted superior numbers as well as air and naval support, but Yamasaki’s men benefited from their stout defensive positions. From the high ground, they could batter the Americans with machine gun and mortar fire or simply roll grenades downhill. As always, the Aleutian weather was also a formidable foe. Freezing rain and howling winds harassed the G.I.s—most of whom were not outfitted with cold weather gear—leading to thousands of cases of trench foot, frostbite and gangrene.

A squadron of American P-38 fighters in flight over the Aleutian Islands. (Credit: Dmitri Kessel/The LIFE Picture Collection/Getty Images)

The turning point in the Battle of Attu came in mid-May, when the outnumbered Japanese fell back to positions near Chichagof Harbor, allowing the Americans’ northern and southern forces to link up with one another. Over the next two weeks, the attackers continued to inch forward, slowly boxing the Japanese into the eastern sector of the island. The fighting was ferocious and bloody, with gains often measured in mere yards. During one action on May 26, an Army private named Joe Martinez led an advance under heavy fire and singlehandedly destroyed several Japanese trenches before being mortally wounded. The New Mexico native would later become the Battle of Attu’s only Medal of Honor winner.

By the end of the month, the Japanese force on Attu had dwindled to around 1,000 exhausted men. Rather than surrender, however, Colonel Yamasaki launched a desperate counterattack. In the early morning hours of May 29, he led hundreds of screaming soldiers in a banzai charge against the American lines. “Every Japanese who could walk took part,” Dashiell Hammett wrote, “some armed only with bayonets tied on the end of sticks.” The human wave attack succeeded in penetrating the American lines, but it was soon routed in fierce hand-to-hand combat. When the Battle of Attu finally ended the following day, fewer than 30 Japanese soldiers surrendered to the Americans. The rest—including Yamasaki—had either died fighting or taken their own lives.

U.S. troops landing on Attu in May 1943.

The clash on Attu would prove to be the only major battle of the Aleutian campaign. The Army and Navy had assumed that Kiska would present the more serious challenge, but when U.S. forces finally invaded the island on August 15, they discovered that the Japanese had already abandoned it weeks earlier. “Nest seized but the bird had flown” read a headline in the New York Times. Securing the island was still an ordeal—the American force suffered several hundred casualties from exposure and Japanese booby troops—but by late August, it was back in American hands.

U.S. military personnel unloading supplies during a beach landing on the Aleutian Islands. (Credit: PhotoQuest/Getty Images)

considered a sideshow to the more high-profile battles in the South Pacific, the Aleutians campaign was a vital early victory for the United States. By reclaiming the Alaskan islands, the Americans opened a potential invasion route to Tokyo that, while never utilized, forced the Japanese to divert manpower and supplies to the North Pacific. Even more crucially, the battle in the icy north had stonewalled Japan’s efforts to advance into the Western Hemisphere. During the remainder of the war, Japanese forces would never again secure a toehold on American soil.