In World War II, the then-primarily Nisei battalion was composed largely of former members of the Hawaii Army National Guard and trained at Camp McCoy, Wisconsin from June 1942 to January 1943.The 100th Infantry Battalion went to Camp Shelby, Mississippi in January 1943 for advanced training and left for overseas in August 1943.

[10] Quote: [Nearly a century later,] "the "Remember Pearl Harbor" 100th Infantry Battalion, and the "Go For Broke" 442d Regimental Combat Team is still the most decorated unit in U.S. military history.

Members of this World War II unit earned over 18,000 individual decorations including over 4,000 Purple Hearts, and 21 Medals of Honor.

The Combat Team earned five Presidential Citations in 20 days of Rhineland fighting, the only military unit ever to claim that achievement.

General of the Army George C. Marshall praised the team saying, "they were superb: the men of the 100/442d... showed rare courage and tremendous fighting spirit... everybody wanted them."

[13] On the morning of 7 December 1941, the Empire of Japan attacked Pearl Harbor, marking the beginning of World War II for the United States.

Chaos ensued in the hours that followed the Pearl Harbor attack, but the 298th and 299th Hawaii National Guard prepared for an invasion, cleared the rubble, donated their blood, and aided the wounded.

[15] At 11:30 a.m. martial law was declared, and Governor Joseph Poindexter told President Franklin D. Roosevelt that his greatest fear was sabotage by the large Japanese population in Hawaii.

The FBI rounded up known Japanese sympathizers, Buddhist priests, language school principals and teachers, civic and business leaders, fishermen, and instructors of Judo and related martial arts.

[17] General Delos Emmons, appointed military governor on 17 December, supported placing Japanese Americans in internment camps and having them reclassified as enemy aliens, but he wanted to give them a chance to prove their patriotism.

[18] As the Battle of Midway was well underway on 4 June 1942, 1,432 Nisei of the Hawaii National Guard boarded the U.S. Army transport USAT Maui, formerly a Matson liner, under the cover of night and were shipped to the mainland without saying goodbye to their family or loved ones.

Immediately following their arrival to Camp McCoy many of the Nisei felt animosity and distrust from fellow soldiers and military and political leaders.

Eventually soldiers were permanently placed into military units, such as Companies A through F, and pushed through physical, marksmanship, and tactical training.

Lieutenant General Mark Wayne Clark, commanding the United States Fifth Army, accepted the offer, and the 100th became a part of the 133rd Infantry Regiment, 34th Infantry Division, in place of the regiment's 2nd Battalion that had been assigned to guard General Eisenhower's headquarters in Oran, North Africa, and took part in training with white soldiers.

The unit advanced 15 miles (24 km) in 24 hours for a week against strong enemy resistance which allowed them to take Benevento, an important rail center and road intersection.

They become blood relations to you and they die before your eyes-not a pleasant, natural death, but an unimaginable kind of mutilation mixed with groans and prayers ending with a gurgling last breath.

To take the Gustav Line, the Allies would have to descend into the Rapido River valley, traverse two miles of open fields filled with landmines, mud, and knee-deep cold water, cross a swift-moving river, and barbed wire and up the steep, rocky slopes, to the 1500-foot peak of Monte Cassino.

At night, A and C companies passed their way through the river reaching the wall where the enemy was located and held their ground under intense fire into the next day.

[32] During the first daylight hours our battalion observation post started with 26 individuals including the artillery liaison team communication people and the intelligence section.

Major Clough was ordered by Colonel Marshall, 133rd Regiment Commander, to commit "B" Company across the open flats at daybreak.

The hill was a key location for it was close to the monastery but the 34th Division's right and left flanks were unable to hold their positions because of heavy German resistance.

"[30] This would be the last time Nisei of the original 100th would see combat at Monte Cassino as they were taken back to San Michele to rest and reorganize.

Lieutenant Young-Oak Kim, a Korean American born in Los Angeles, California, and Nisei PFC Irving Akahoshi from the 100th volunteered for the mission and captured two German soldiers.

They (100th Battalion) wiped out the last heavy German resistance we met some 12 miles south of Rome and then it was practically a walk into the city.

[30] Instead, the 100th was taken 40 miles (64 km) northwest of Rome to Civitavecchia where on 11 June 1944, the 100th was assigned to the newly arrived 442nd Regimental Combat Team as its 1st Battalion.

[39] The battalion headquarters is at Fort Shafter, Hawaii, with subordinate units based in Hilo, American Samoa,[40] Saipan, Guam, and Washington.

[56] On 5 October 2010, Congress approved the granting of the Congressional Gold Medal to the 442nd Regimental Combat Team and the 100th Infantry Battalion, as well as the 6,000 Japanese Americans who served in the Military Intelligence Service during the war.

[58] In 2012, the surviving members of the 442nd RCT were made chevaliers of the French Légion d'Honneur for their actions contributing to the liberation of France during World War II and their heroic rescue of the Lost Battalion outside of Biffontaine.