The Aleutian Islands campaign (Japanese: アリューシャン方面の戦い, romanized: Aryūshan hōmen no tatakai) was a military campaign fought between 3 June 1942 and 15 August 1943 on and around the Aleutian Islands in the American Theater of World War II during the Pacific War. It was the only military campaign of World War II fought on North American soil.

The islands' strategic value was their ability to control Pacific transportation routes as US General Billy Mitchell stated to the U.S. Congress in 1935, "I believe that in the future, whoever holds Alaska will hold the world. I think it is the most important strategic place in the world." The Japanese reasoned that their control of the Aleutians would prevent a possible joining of forces by the Americans and the Soviets and future attack on Japan proper via the Kuril Islands. Similarly, the US feared that the islands could be used as bases from which to launch air raids on West Coast cities such as Anchorage, Seattle, San Francisco, or Los Angeles.

Following two aircraft carrier-based attacks on the American naval base at Dutch Harbor, the Imperial Japanese Navy occupied the islands of Attu and Kiska, where the remoteness of the islands and the challenges of weather and terrain delayed a larger American-Canadian force sent to eject them for nearly a year. A battle to reclaim Attu was launched on 11 May 1943 and completed after a final Japanese banzai charge on 29 May. On 15 August 1943 an invasion force landed on Kiska in the wake of a sustained three-week barrage, only to discover that the Japanese had withdrawn from the island on 29 July. The campaign is known as the "Forgotten Battle" because it has been overshadowed by other events in the war.

Many military historians believe that the Japanese invasion of the Aleutians was a diversionary or feint attack during the Battle of Midway that was meant to draw out the US Pacific Fleet from Midway Atoll, as it was launched simultaneously under the same commander, Isoroku Yamamoto. Some historians have argued against that interpretation and believe that the Japanese invaded the Aleutians to protect their northern flank and did not intend it as a diversion.

Before the Empire of Japan entered World War II, the Imperial Japanese Navy had gathered extensive information about the Aleutians but had no up-to-date information regarding military developments on the islands. Admiral Isoroku Yamamoto provided the Japanese Northern Area Fleet, commanded by Vice Admiral Boshirō Hosogaya, with a force of two non-fleet aircraft carriers, five cruisers, twelve destroyers, six submarines, and four troop transports, along with supporting auxiliary ships. With that force, Hosogaya was to launch an air attack against Dutch Harbor then follow with an amphibious attack upon Adak Island, 480 miles (770 km) to the west. Hosogaya was instructed to destroy whatever American forces and facilities were found on Adak, but the Japanese did not know the island was undefended. Hosogaya's troops were to return to their ships and become a reserve for two additional landings: the first on Kiska, 240 miles (390 km) west of Adak, the other on the Aleutians' westernmost island, Attu, 180 miles (290 km) west from Kiska.

Because the Office of Naval Intelligence had broken the Japanese naval codes, Admiral Chester Nimitz learned by May 1942 of Yamamoto's plans, including the Aleutian invasion, the strength of both Yamamoto's and Hosogaya's fleets, and Hosogaya's plan attack the Aleutians on 1 June or shortly thereafter.

As of 1 June, the US military strength in Alaska stood at 45,000 men, with about 13,000 at Cold Bay (Fort Randall) on the tip of the Alaska Peninsula and at two Aleutian bases: Dutch Harbor on Unalaska Island, 200 miles (320 km) west of Cold Bay, and the recently built Fort Glenn Army Air Base on the island of Umnak 70 miles (110 km) west of Dutch Harbor. Army strength, less air force personnel, at those three bases totaled no more than 2,300, composed mainly of infantry, field and anti-aircraft artillery troops, and a large construction engineer contingent, which was used in the construction of bases. The Army Air Force's Eleventh Air Force consisted of 10 B-17 Flying Fortress heavy bombers and 34 B-18 Bolo medium bombers at Elmendorf Airfield, and 95 P-40 Warhawk fighters divided between Fort Randall and Fort Glenn. The forward headquarters was set up at Fort Geely, while the rear units were stationed at Fort Richardson. The naval commander was Rear Admiral Robert A. Theobald, commanding Task Force 8 afloat, who as Commander North Pacific Force (ComNorPac) reported to Nimitz in Hawaii. Task Force 8 consisted of five cruisers, thirteen destroyers, three tankers, six submarines, as well as naval aviation elements of Fleet Air Wing Four.

When the first signs of a possible Japanese attack on the Aleutians were known, the Eleventh Air Force was ordered to send out reconnaissance aircraft to locate the Japanese fleet reported heading toward Dutch Harbor and attack it with bombers, concentrating on sinking Hosogaya's two aircraft carriers. Once the enemy planes were removed, Naval Task Force 8 would engage the enemy fleet and destroy it. On the afternoon of 2 June, a naval patrol plane spotted the approaching Japanese fleet, reporting its location as 800 nautical miles (1,500 km; 920 mi) southwest of Dutch Harbor. Eleventh Air Force was placed on full alert. Shortly thereafter bad weather set in, and no further sightings of the fleet were made that day.

Before the attack on Dutch Harbor, the Army's 4th Infantry Regiment, under command of Colonel Percy E. LeStourgeon, was established at Fort Richardson. LeStourgeon had previously designed a layout of base facilities—such as isolation of weapons and munitions depots—to protect against enemy attack.

According to Japanese intelligence, the nearest field for land-based American aircraft was at Fort Morrow Army Airfield on Kodiak, more than 600 miles (970 km) away, and Dutch Harbor was a sitting duck for the strong Japanese fleet, carrying out a coordinated operation with a fleet that was to capture Midway Island.

Making use of weather cover, the Japanese made a two-day aerial bombing of continental North America for the first time in history. The striking force was composed of Nakajima B5N2 "Kate" torpedo bombers from the carriers Jun'yō and Ryūjō. However, only half of the striking force reached their objective. The rest either became lost in the fog and darkness and crashed into the sea or returned to their carriers. Seventeen Japanese planes found the naval base, the first arriving at 05:45. As the Japanese pilots looked for targets to engage, they came under intense anti-aircraft fire and soon found themselves confronted by Eleventh Air Force fighters sent from Fort Glenn. Startled by the American response, the Japanese quickly released their bombs, made a cursory strafing run, and left to return to their carriers. As a result, they did little damage to the base.

On 4 June the Japanese returned to Dutch Harbor. This time, the Japanese pilots were better organized and prepared. When the attack ended that afternoon, Dutch Harbor oil storage tanks were burning, the hospital was partly demolished, and a beached barracks ship was damaged. Although American pilots eventually located the Japanese carriers, attempts to sink the ships failed because bad weather set in that caused the US pilots to lose all contact with the Japanese fleet. However, the weather caused the Japanese to cancel plans to invade Adak with 1,200 men.

The Japanese invasions and occupations of Kiska on 6 June and Attu on 7 June shocked the American public, as the continental United States was invaded for the first time in 130 years since 1815 (during the War of 1812). The invading forces initially met little resistance from the local Unangax, also known as Aleuts. Though the U.S. Navy had offered to evacuate Attu in May 1942, the Attuan Unangax chief declined. Little changed for the Unangax under Japanese occupation until September 1942 when Japan's Aleutian strategy shifted. It was at this point that the Unangax were taken to Hokkaido, Japan, and placed in an internment camp.

The invasion of Attu and imprisonment of the local Unangax became the justification for the United States' policy of forcible evacuation of the Unangax in the Aleutian Islands. Unangan civilians were placed in internment camps in the Alaska Panhandle.

Through the rest of the summer of 1942, aerial raids by either side could be flown only when the weather permitted. Japan installed a radar warning system on the islands and continued to resupply them, despite heavy disruptions against its shipping by US bombers and submarines. The establishment of American air bases in Umnak and Cold Bay would add to the threat faced by the Japanese.

Many Americans feared that the Japanese would use the islands as bases to strike within range along the rest of the West Coast. Although the West Coast was subject to attack several times in 1942 (including unrestricted submarine warfare in coastal waters; the bombardment of Ellwood in California; and the bombardment of Fort Stevens in Oregon), the Aleutian Islands campaign of June 1942 was the first major operation by a foreign enemy in the American Theater. Lieutenant Paul Bishop of the 28th Bombardment Group recalled:

General Simon B. Buckner Jr. [of the Alaska Defense Command] said to us that the Japanese would have the opportunity to set up airbases in the Aleutians, making coastal cities like Anchorage, Seattle, and San Francisco vulnerable within range to attack by their bombers. The fear of that scenario was real at the time because the Japanese were nearly invincible and ruthless in Asia and the Pacific. We knew that they bombed China relentlessly and by surprise on Pearl Harbor, so we had to make sure it wouldn't happen here in the continental U.S. similar to what the Germans did over London and Coventry.

Lieutenant Bob Brocklehurst of the 18th Fighter Squadron stated:

[T]he impression we were given — and this was voiced oral stuff — was that we had nothing to stop the Japanese. [Our commanding officers] figured that the Japanese, if they wanted to, could have come up the Aleutians, taken Anchorage, and come down past down Vancouver to Seattle, Washington.

On 31 August 1942 American forces attacked Adak Island after scouting it two days earlier. To keep the Japanese on Kiska occupied, missions were flown there by bombers from the Eleventh Air Force. They were escorted by fighter aircraft, including P-38s from Umnak over 600 miles away. Runway construction began immediately following the American landing. After 10 September, fighters and bombers were moved into the new Adak airbase and used to launch more bombing raids against Japanese positions on Kiska.

From September to November, American air raids were able to keep the total number of enemy aircraft low, usually under 14 frames, despite persistent attempts to reinforce their number by the Japanese. Without supporting carriers in the area, the Japanese were unable to dislodge the American forces on Adak. Even when they had a few air assets to spare, the Japanese generally avoided direct combat. Other supplies were also beginning to run low. After evacuating Attu, the Japanese contemplated occupying and setting up a new base on either the Semichis or Amchitka but were not able to carry out those plans.

In February 1943, the Americans successfully occupied Amchitka and built an airstrip there. Their main losses were a result of bad weather. Ground attack missions were flown from the new island base, starting with P-38s and P-40s before bombers also joined in. Their targets included radar installations, parked aircraft, anti-aircraft artillery positions, railway, submarine base, and moored vessels. The bombings further reduced Japan's ability to supply its bases, hampered its construction of landing strips on Attu and Kiska, and facilitated the recapture of those two islands later that year. In April 1943 Japanese surface convoys made their final attempt to break through American naval blockade and resupply troops on Attu and Kiska but were forced to abort after being defeated in battle. Future Japanese resupply missions would be conducted exclusively by submarines and limited by how much materiel they could bring.

Navy submarines and surface ships had also been patrolling the area. Kiska Harbor was the main base for Japanese ships in the campaign and several were sunk there, some by warships but mostly in air raids. On 5 July 1942 the submarine Growler, under command of Lieutenant Commander Howard Gilmore, attacked three Japanese destroyers off Kiska. She sank one and heavily damaged the others, killing or wounding 200 Japanese sailors. Ten days later, Grunion was attacked by three Japanese submarine chasers in Kiska Harbor, with two of the patrol craft sunk and one other damaged. On 12 May 1943 the Japanese submarine I-31 was sunk in a surface action with the destroyer Edwards 5 mi (4.3 nmi; 8.0 km) northeast of Chichagof Harbor.

At least three Japanese submarines were sunk near Kiska in June 1943, reportedly on the 11th, 13th, and 22nd.

A cruiser and destroyer force under Rear Admiral Charles "Soc" McMorris was assigned to eliminate the Japanese supply convoys. They met the Japanese fleet in March 1943. One American cruiser and two destroyers were damaged, and seven US sailors were killed. Two Japanese cruisers were damaged, with 14 men killed and 26 wounded. Japan thereafter abandoned all attempts to resupply the Aleutian garrisons by surface vessels, and only submarines would be used.

On 11 May 1943 American forces commenced Operation Landcrab to recapture Attu. The invasion force included the 17th and 32nd Infantry regiments of the 7th Infantry Division and a platoon of scouts recruited from Alaska, nicknamed Castner's Cutthroats. The army air force flew more than 500 sorties in a 20-day period to support the invasion. A shortage of landing craft, unsuitable beaches, and equipment that failed to operate in the appalling weather made it difficult however for the Americans to exert force against the Japanese. Soldiers suffered from frostbite because essential cold-weather supplies could not be landed, and soldiers could not be relocated to where they were needed because vehicles could not operate on the tundra. Rather than engage the Americans where they landed, Colonel Yasuyo Yamasaki had his forces dig into the high ground far from the shore. That resulted in fierce combat, with a total of 3,829 US casualties, with 549 killed, 1,148 wounded, and another 1,200 suffering severe injuries from the cold weather. Also, 614 Americans died from disease and 318 from miscellaneous causes, mainly Japanese booby traps or friendly fire.

On 29 May 1943 without warning the remainder of Japanese forces attacked near Massacre Bay. Recorded as one of the largest banzai charges of the Pacific campaign, Yamasaki penetrated so deep into US lines that Japanese soldiers encountered rear-echelon units of the Americans. After furious, brutal, often hand-to-hand combat, the Japanese force was virtually exterminated. Only 28 Japanese soldiers were taken prisoner, none of them were officers. American burial teams counted 2,351 Japanese dead, but it was thought that hundreds more had been buried by bombardment during the battle.

With its loss of Attu to U.S. forces, Japan was deprived of its only remaining airstrip in the Aleutians, a disadvantage that it could not compensate for because Japanese aviation units were entirely ground-based.

On 15 August 1943 an invasion force of 34,426 Canadian and American troops landed on Kiska. Castner's Cutthroats were part of the force, but the invasion consisted mainly of units from the 7th Infantry Division. The force also included about 5,300 Canadians, mostly from the 13th Canadian Infantry Brigade of the 6th Canadian Infantry Division, and the 1st Special Service Force, a 2,000-strong Canadian-American commando unit formed in 1942 in Montana and trained in winter warfare techniques. The force included three 600-man regiments: the 1st was to go ashore in the first wave at Kiska Harbor, the 2nd was to be held in reserve to parachute where needed, and the 3rd was to land on the north side of Kiska on the second day of the assault. The 87th Regiment of the 10th Mountain Division, the only major U.S. force specifically trained for mountain warfare, was also part of the operation.

Royal Canadian Air Force No. 111 and No. 14 Squadrons saw active service in the Aleutian skies and scored at least one aerial kill on a Japanese aircraft. Additionally, three Canadian armed merchant cruisers and two corvettes served in the Aleutian campaign but did not encounter enemy forces.

It is likely that the main Japanese forces left Kiska on the night of 28 July when its radio became silent. During the subsequent two weeks, the Army Air Force and the navy bombed and shelled the abandoned positions. The day before the withdrawal, the US Navy fought an inconclusive and possibly meaningless Battle of the Pips 80 mi (70 nmi; 130 km) to the west.

The allied invasion forces encountered no opposition on 15 August, but their total casualties would in the end number 313 due to friendly fire, vehicle accidents, Japanese booby traps and explosives, disease and frostbite. Like Attu, Kiska offered an extremely hostile environment.

The loyal courage, vigorous energy and determined fortitude of our armed forces in Alaska—on land, in the air and on the water—have turned back the tide of Japanese invasion, ejected the enemy from our shores and made a fortress of our last frontier. But this is only the beginning. We have opened the road to Tokyo; the shortest, most direct and most devastating to our enemies. May we soon travel that road to victory.

— Lieutenant General Simon Bolivar Buckner Jr., a few months after the Aleutian Islands campaign

Although plans were drawn up for attacking northern Japan, they were not executed. Over 1,500 sorties were flown against the Kuriles before the end of the war, including the Japanese base of Paramushir, which diverted 500 Japanese planes and 41,000 ground troops.

The battle also marked the first time that Canadian conscripts were sent to a combat zone in World War II. The government had pledged not to send draftees "overseas", which it defined as being outside North America. The Aleutians were considered to be North American soil, which enabled the Canadian government to deploy conscripts without breaking its pledge. There were cases of desertion before the brigade sailed for the Aleutians. In late 1944, the government changed its policy on draftees and sent 16,000 conscripts to Europe to take part in the fighting. The battle also marked the first combat deployment of the 1st Special Service Force, but it did not see any action.

In the summer of 1942, the Americans recovered the Akutan Zero, an almost-intact Mitsubishi A6M2 Zero fighter, which enabled the Americans to test-fly the Zero and contributed to improved fighter tactics later in the war.

During the campaign, two cemeteries were established on Attu to bury those killed in action: Little Falls Cemetery, at the foot of Gilbert Ridge, and Holtz Bay Cemetery, which held the graves of Northern Landing Forces. After the war, the tundra began to take back the cemeteries and so in 1946, all American remains were relocated as directed by the soldier's family or to Fort Richardson near Anchorage, Alaska. On 30 May 1946 a Memorial Day address was given by Captain Adair with a 21-gun salute and the sounding of Taps. The Decoration of Graves was performed by Chaplains Meaney and Insko.

Many of the United States locations involved in the campaign, either directly or indirectly, have been listed on the National Register of Historic Places, and several have been designated National Historic Landmarks. The battlefield on Attu and the Japanese occupation site on Kiska are both National Historic Landmarks and are included in the Aleutian Islands World War II National Monument. Surviving elements of the military bases at Adak, Umnak, and Dutch Harbor are National Historic Landmarks. The shipwrecked SS Northwestern, badly damaged during the attack on Dutch Harbor, is listed on the National Register, as is a crash-landed B-24D Liberator on Atka Island.

The 2006 documentary film Red White Black & Blue features two veterans of the Attu Island campaign, Bill Jones and Andy Petrus. It is directed by Tom Putnam and debuted at the 2006 Locarno International Film Festival in Locarno, Switzerland, on 4 August 2006.

Dashiell Hammett spent most of World War II as an Army sergeant in the Aleutian Islands, where he edited an Army newspaper. He came out of the war suffering from emphysema. As a corporal in 1943, he co-authored The Battle of the Aleutians with Corporal Robert Colodny under the direction of Infantry Intelligence Officer Major Henry W. Hall.

• Military history of the Aleutian Islands
• Organization of the Imperial Japanese Navy Alaskan Strike Group
• Paul Nobuo Tatsuguchi, Japanese doctor stationed on Attu
• Report from the Aleutians, a 1943 American documentary propaganda film about the campaign, directed by John Huston

• Vidal, Gore (1946), Williwaw, New York: E. P. Dutton.

Wikimedia Commons has media related to Aleutian Islands campaign.

• Logistics Problems on Attu by Robert E. Burks.
• The short film "Operations at Amchitka, Attacks on Attu" is available for free viewing and download at the Internet Archive.
• Aleutian Islands Chronology
• Aleutian Islands War
• Red White Black & Blue – feature documentary about The Battle of Attu in the Aleutians during World War II
  • PBS Independent Lens presentation of Red White Black & Blue – The Making Of and other resources
• ”Attu: North American Battleground of World War II”, a National Park Service Teaching with Historic Places (TwHP) lesson plan
• Animated Maps of the Aleutians Campaign Archived September 17, 2011, at the Wayback Machine
• Attu, Aleutian Islands, Alaska WW-II KIA
• US losses at Kiska