So Yanamura volunteered to join the Army to prove his loyalty.
Nearly 70 years later, that same government honored him and the thousands of other Japanese-Americans who served in World War II with one of its most elite rewards: the Congressional Gold Medal.
Starting this weekend in New Orleans, the medal is going on a yearlong national tour that will spread the stories of the veterans, their sacrifices and their triumphs. The tour is organized by the Smithsonian in partnership with the National Veterans Network, a coalition of Japanese-American veteran and civic organizations.
Irene Hirano Inouye said her late husband — U.S. Sen. Daniel Inouye, who lost his right arm fighting with the 442nd Regimental Combat Team in Italy — saw the tour as an important way to tell others what happened.
"For a lot of younger people, World War II is like ancient times," Inouye said in a telephone interview. "We have to remember that there are a lot of younger people who just have not been exposed to the story."
Congress last year awarded the medal collectively to men who served in three segregated units of mostly Japanese-Americans: the 100th Infantry Battalion — nicknamed the Purple Heart Battalion because of the casualties it endured— the 442nd Regimental Combat Team and the Military Intelligence Service. Besides these units, it was rare for Japanese-Americans to serve in other parts of the U.S. military.
The 442nd — which absorbed the 100th Infantry during the war — is the most highly decorated military unit in U.S. history for its size and length of service. Soldiers of the 442nd and 100th both fought in Europe.
Linguists in the Military Intelligence Service served in the Pacific, interrogating Japanese prisoners and deciphering maps, soldier diaries and other documents.
Japanese-Americans were at first not allowed to serve, rendered ineligible for the draft because of their "enemy" status.
But in 1943, the government decided to allow some to volunteer.
The Army put out a call for 1,500 to come forward; more than 10,000 raised their hands.
Yanamura's homeroom teacher (also Japanese-American) told his class all 18-year-olds should volunteer to prove their loyalty.
"I went home from school and talked to my father. He said, without any hesitation, 'You must volunteer. You got to show your loyalty,'" Yanamura said.
He first joined the 442nd but switched to the MIS after realizing he would be more useful as a linguist than as an infantryman.
He was awarded the Bronze Star for using a loudspeaker to successfully coax 1,500 civilians and 150 soldiers in the village of Maehira to surrender during the Battle of Okinawa.
He never spoke much of his actions until recently, modestly saying "we really didn't do much." And he at first doubted whether he should be honored by the same award given to George Washington and other American heroes.
But he's come to accept the medal as an apology to men who risked their lives even though their country treated them as enemies and imprisoned their families in concentration camps.
"Despite all that, we still went ahead and performed outstandingly," he said. "From that standpoint, I guess, we should be thankful that the recognition has been made, though a long time later."
Inouye said her husband, who died last month at the age of 88, would tell school groups the U.S. continues to evolve and grow, noting he became a senator even though he was once declared an enemy alien.
"A lot of those lessons are what the real meaning of an exhibition like this is," she said.
Yanamura, now 88, and Inouye will attend a ceremony opening the exhibition on Saturday at the National World War II Museum in New Orleans. The medal will travel to museums in Honolulu, Los Angeles, San Francisco, Portland, Ore., Chicago and Houston over the next year.