Quite a few of them enlisted in the military or were drafted from the camps. Can you imagine that, you and your family is being held prisoner and you get drafted? Not that some people didn't resist the policies but most of them didn't.

Many people have heard of units like the 442nd "Go for Broke" Regimental Combat Team. This unit was founded by Nisei (2nd generation Americans of Japanese ancestry) from Hawaii. There was also the 100th Infantry Battalion that served in the ETO during WWII. Those were perhaps the most highly decorated units in the Army. They had something to prove and they did.

Fewer people know of the Japanese translators who served with the Army in the Pacific during the war. As the link states,

The Japanese felt secure in using their military language without using code, assuming that U.S. Forces did not have sufficient knowledge of the Japanese language to intercept and understand their messages. It was therefore imperative that the presence of Japanese Americans with Allied combat troops in the Pacific Theater be kept a secret . Therefore, contrary to the publicity given to the brave exploits of the Japanese American soldiers fighting in Europe, the exploits of Japanese American soldiers in the Pacific Theater received no publicity despite the high praises given to them in classified communication.

Maj Gen C.A. Willoughby , Ass’t Chief of Staff, G-2,GHQ , Far East Command, stated the Nisei"…saved over 1,000,000 American lives and shortened the war by two years…they collected information on the battlefield, they shared death in battle…in all they handled between two and three million (Japanese) documents. The information received through their special skills proved invaluable to our battle forces". Colonel Sydney F. Mashbir, who headed General MacArthur’s Allied Translator and Interpreter Section (ATIS), GHQ said in praise of Nisei, "The United States of America owes a debt to these men and to their families which it can never fully repay…They were worthy ,as individuals and as a group, of the highest praise for their invaluable contributions to the success of Allied arms."

Here's a timeline of events on the subject.