Timeline of 100th Infantry Battalion and 442nd Regimental Combat Team in WWII
- 100thibvohana
- Sep 23
- 7 min read
When Japan attacked Pearl Harbor on December 7, 1941, the United States entered World War II, and life changed dramatically for Americans of Japanese ancestry (AJA). Despite facing discrimination, suspicion, and mass incarceration, thousands of Japanese Americans were drafted or volunteered to serve in the U.S. military. By war’s end, nearly 10,000 men served in the combined 100th Infantry Battalion (100th INF BN) and 442nd Regimental Combat Team (442nd RCT), which are recognized as among the most decorated units in military history.
Timeline of 100th Infantry Battalion and 442nd Regimental Combat Team in World War II
This timeline, developed by “The 100TH, Seeds of Aloha” film team led by producer, Steve Sue, highlights the journey of the 100th Infantry Battalion and the 442nd Regimental Combat Team, whose courage and sacrifice helped shape both military history and the broader story of America’s struggle for equality and civil rights.
▶︎ 1941 – 1942:
Pearl Harbor and Discrimination
December 7, 1941: The attack on Pearl Harbor placed Hawai‘i under martial law.
January 5, 1942: The Selective Service classified all draft-age males of Japanese descent as category IV-C “aliens of enemy nationality.” While many AJAs sought to prove they were loyal Americans, the onus fell especially on the Japanese Americans already in the U.S. Army, like the approximately 1,500 members of Hawai‘i’s 298th and 299th Infantries in Hawai‘i and a similar number serving in other posts in the United States.
February 19, 1942: Executive Order 9066 authorized the forced removal of AJA from the West Coast.
By the end of the war, the United States had incarcerated 120,000 people of Japanese ancestry, approximately two-thirds of whom were U.S. citizens, while the remaining one-third were Japanese immigrants legally barred from citizenship.
Approximately 2,000 residents from Hawai‘i were incarcerated, mostly Japanese immigrants or community leaders.
German and Italian Americans faced restrictions as well.
Formation of the 100th Infantry Battalion (Separate)
May 28, 1942: The “Hawaiian Provisional Infantry Battalion” is formed with already-enlisted U.S. Army AJA soldiers in Hawai‘i who had been serving in the 298th and 299th Infantry Regiments of the Hawai‘i National Guard, activated reservists of the Reserve Corps (USAR), and active duty soldiers, as well as some members of the 3rd Combat Engineer Battalion of the 24th Infantry Division and 65th Combat Engineer Battalion of the 25th Infantry Division. The War Department, fearing that the Japanese forces would invade Hawai‘i after the impending battle at Midway, secretly ordered military governor General Delos Emmons to send the American soldiers of Japanese descent to the mainland as soon as possible.
June 5, 1942: The 1,432 men in the Hawaiian Provisional Infantry Battalion departed Hawai‘i in secrecy to Oakland, CA.
June 12, 1942: The Hawaiian Provisional Infantry Battalion was activated and redesignated the “100th Infantry Battalion (Separate).” The unit was sent to Camp McCoy, Wisconsin, for training. By December 1942, about 60 men were transferred from the 100th to Camp Savage, Minnesota, to train at the Military Intelligence Service (MIS) Language School. On January 6, 1943, the 100th INF BN (SEP) left for Camp Shelby, Mississippi, for advanced training, and later conducted field maneuvers at Camp Claiborne in Louisiana until June 1943.
▶︎ 1943 – 1945:
Formation of the 442nd Regimental Combat Team
January 1943: Impressed by the outstanding training performance of the 100th, the War Department announced plans to organize a combat team of loyal American citizens of Japanese ancestry.
The call went out for 1,500 volunteers from Hawai‘i, but nearly 10,000 men responded, including members of the Varsity Victory Volunteers (VVV), who had formed the VVV after being discharged from the Hawai‘i Territorial Guard following the Pearl Harbor attack.
A quota of 3,000 was established in the continental United States (CONUS), but the response was 1,200 volunteers.
Consequently, the quotas were reversed, with about two-thirds (2,686 men) volunteering from Hawai‘i and one-third (~1,500 men) from CONUS. Most of the CONUS volunteers enlisted from incarceration camps.
March 28, 1943: Hawai‘i held a farewell ceremony at ʻIolani Palace for the departing soldiers of the 442nd Regimental Combat Team — a stark contrast to the solemn manner in which the 100th Infantry Battalion (Separate), then known as the Hawaiian Provisional Infantry Battalion, had quietly departed in secrecy on June 5, 1942.
May 1943: Basic training began at Camp Shelby, Mississippi, for the new AJA recruits of the 442nd RCT to prepare for combat.
First Combat and Heavy Losses for the 100th INF BN (SEP)
September 22, 1943: The 100th INF BN (SEP), attached to the 133rd Infantry Regiment, 34th Infantry Division (ID), landed on the beaches at Salerno, Italy, with just over 1,300 soldiers. It headed into combat in pursuit of retreating German forces on Sept. 26., and engaged in active combat for the first time on Sept. 29, when Sgt. Shigeo “Joe” Takata became the first member of the 100th to be killed in action and the first to receive the Distinguished Service Cross.
September 1943 – January 1944: The 100th fought with the 34th ID during the early stages of the Allied campaign in Italy, engaging in some of the fiercest battles across Salerno, Benevento, Pozzilli, and Monte Cassino. The 100th earned the nickname, “The Purple Heart Battalion” due to the heavy casualties it sustained during its first five months of intense combat in these critical early offensives.
January 20, 1944: With a growing need for trained AJA men to serve in the segregated units of the 100th INF BN (SEP) fighting in Italy, or the 442nd RCT which was preparing for deployment and sending replacements to the casualty-depleted 100th, Selective Service induction of AJA resumed. The War Department announced the reinstatement of general Selective Service procedures for American citizens of Japanese descent, stating that “the excellent showing which the [442nd] Combat Team has made in training, and the outstanding record achieved by the 100th Battalion (a former Hawaiian National Guard unit) now fighting in Italy were major factors in the adoption of the present plan.”
February - May 1944: By early February 1944, injuries and deaths reduced the 100th INF BN (SEP) to just 521 men. After Cassino, the first group of officers and enlisted men from the 442nd RCT arrived in Italy March 1944, transferring to the 100th as replacements to replenish the depleted battalion. Following its participation in the Anzio Campaign, the 100th INF BN (SEP) advanced toward Lanuvio on May 27, helping to break German lines and contributing to the liberation of Rome on June 5.
First Combat for the 442nd RCT and United as the 100th/442nd
May 28, 1944: The 442nd RCT landed in Naples, Italy, joining the battle-tested 100th INF BN (SEP) at Civitavecchia, northwest of Rome, in June 1944.
June 11, 1944: The 100th was attached to the 442nd RCT, serving as the 1st Battalion of 442nd, but retaining its unit designation as the 100th Infantry Battalion (Separate). The 442nd RCT entered combat for its first time on June 26, when the 100th and 442nd went into combat near Belvedere, Italy. The 100th INF BN (SEP) was awarded its first Presidential Unit Citation for its outstanding performance of duty in action on June 26 and 27 1944, in the vicinity of Belvedere and Sassetta, Italy.
August 10, 1944: The 100th INF BN (SEP) was redesignated as “100th Battalion, 442nd Infantry,” officially integrated as the 1st Battalion of 442nd RCT, but retained its numeric “100th” designation, because of its outstanding combat record.
The combined 100th/442nd fought in some of the toughest European campaigns, including:
June – July 1944: Battles at Belvedere, Hill 140 and Leghorn (Livorno) in Italy.
October 1944: Rhineland Campaign battles in the Vosges Mountains, France, including the liberation of Bruyères and Biffontaine, and the rescue of the “Lost Battalion,” where the 100th/442nd rescued 211 members of the 1st Battalion, 141st Infantry from Texas, at tremendous cost.
November 1944 – March 1945: The Maritime Alps sector of the Rhineland Campaign, also called the “Champagne Campaign,” in southern France. In March 1945, the 522nd Field Artillery Battalion, originally part of the 442nd RCT, was detached and sent to fight in Germany, where they helped liberate Dachau subcamps.
April – May 1945: The 100th/442nd fought across northern Italy in the battles to break through the Gothic Line and into the Po Valley, across Mt. Folgorito, Carrara, Fosdinovo, and Aulla.
Composed primarily of AJA soldiers from Hawai‘i, the 100th Infantry Battalion, along with the 442nd Regimental Combat Team, became one of the most decorated units in U.S. military history. Through their courage, tremendous sacrifice, and outstanding service in World War II, they earned respect worldwide, and helped pave the way for greater acceptance and civil rights for Japanese Americans in the decades that followed.
▶︎ For a more detailed timeline of the 100th Infantry Battalion, please visit our Education Center at https://www.100thbattalion.org/learn/timeline/
▶︎ Timeline published with permission from "The 100TH, Seeds of Aloha" film producer, Steve Sue. "The 100TH, Seeds of Aloha" is part of Project Shaka (https://projectshaka.com/), a nonprofit trilogy of educational films on the Aloha Spirit. This film tells the powerful story of the 100th Infantry Battalion, a WWII unit predominately made up of Americans of Japanese descent (AJAs) from Hawaiʻi, which fought heroically in Europe, earning the nickname, “The Purple Heart Battalion.” After devastating losses, the 100th INF BN combined with the 442nd RCT to become one of the most decorated units in U.S. military history. The film is more than a tale of war – it’s a testament to the 100th/442nd soldiers who raised the bars on heroism and valor through applying the Spirit of Aloha, both during the war and for 80 years after. For more on the film, or to support "The 100TH, Seeds of Aloha," now in production for a 2026 release, please visit their website at https://100thfilm.com/.