On May 18, Gotham Books, an imprint of Penguin USA, will publish Robert Asahina’s “Just Americans: How Japanese Americans Won a War at Home and Abroad.” The book is a history of the most decorated unit in the American Army in World War II for its size and length of service – the 442d Regimental Combat Team, a segregated unit of Japanese Americans. About half of the regiment had come out of the “relocation camps” where their families had been confined after Pearl Harbor.

The New York Sun asked Mr. Asahina, its deputy managing editor, about how some of the topics in the book – the challenges faced by immigrant groups, the allegations of “dual loyalty,” the war powers of the president – were not just historical matters but pressing current concerns.

The Sun: When you sat down to write “Just Americans,” did you realize how topical the book would be by the time it was published?

Mr. Asahina: I began the proposal for my book in August 2001. I had completed a first draft within a month, and then suddenly it was September 11. I rewrote the proposal that fall, after my wife and I went to France, where I did some research for the book. A few weeks later my agent sent the proposal to publishers, and Gotham wound up buying the book.

Everyone I spoke to about my proposal knew about the “relocation” – in which Japanese Americans in California, Oregon, Washington, and parts of Arizona lost their homes, jobs, and property, and were forced to live in camps. But no one knew about the 442d. Until I started researching and writing, I didn’t know much about it – or about its predecessor, the 100th Battalion, a segregated unit of Japanese Americans from Hawaii. As I did more research, I realized that the story of the “relocation” couldn’t be understood without understanding what Japanese-American soldiers did – by virtue of their heroism in battle – to free their families from confinement at home. And this is a story that is scarcely known at all.

The Sun: How does “Just Americans” tie in with the immigration debate that is going on today in America? And with concerns over homeland security?

Asahina: In 1942, immediately after Pearl Harbor, Japanese Americans were regarded as security threats, even though most of them were American citizens by birth. Today many people are concerned about Arab and Muslim Americans, who in turn worry about “racial profiling.” What is remarkable about the experience of Japanese Americans in World War II is that there was no “racial profiling” at all. The “relocation” simply swept up 110,000 Japanese Americans on the mainland with no distinctions whatsoever being made between men and women, between citizens and non-citizens, between 60-year-old men and 6-month-old babies. What is even more remarkable is that this massive suspension of due process and equal protection of the law was justified by “military necessity.” Yet an even larger population of Japanese Americans in Hawaii was not “relocated” from the islands, which were in a real war zone.

The Sun: But didn’t the courts uphold the power of the President to undertake this kind of action in wartime?

Asahina: Yes, but the Supreme Court decision in Korematsu, which affirmed the doctrine of “military necessity,” is now generally regarded as one of the worst decisions in American constitutional history. Three dissenting justices pointed out at the time that “military necessity” was so nebulous that it could justify virtually anything, even though there was no factual basis for the doctrine. There was no proof that Japanese Americans as a group were disloyal. And a half-century later, in Adarand Constructors, Inc. v. Pena (1995), eight of the nine Justices explicitly called Korematsu a mistake – though they did not overturn it.

The Sun: How does the 442d fit into this legal story?

Asahina: The Korematsu decision was handed down in December 1944. But long before then, within a year or so after Pearl Harbor, officials in the Roosevelt Administration were conceding that there was no “military necessity” for the relocation. When the 442d was formed, the illogic of asking Japanese American soldiers to die for a country that was incarcerating their families was becoming increasingly clear to almost everyone in the government and the military.

But President Roosevelt personally insisted on continuing the “relocation,” even though most of his top advisers – including Secretary of War Stimson, Assistant Secretary of War John J. Mc-Cloy, Attorney General Francis Biddle, and Interior Secretary Harold Ickes (whose department ran the “relocation camps”) – thought the camps should be closed down and the Japanese Americans freed. It was not until after the November 1944 elections – but be fore the Supreme Court decision in Korematsu – that Roosevelt agreed to end the “relocation.” And the reason Stimson cited after meeting with the president had nothing to do with the Constitution. It had to do with the record of the 442d in battle.

The Sun: Why isn’t this story better known?

Asahina: At one time it actually was. There was a Hollywood movie called “Go For Broke” (the motto of the 442d) in 1951, and James Michener wrote about Japanese American soldiers in his 1959 best seller, “Hawaii.” But since then, the story of Japanese Americans as victims during the “relocation” has supplanted the story of Japanese Americans as heroes in battle. What I call the “post-civil rights perspective” has led us to look at minority groups in America as victims who advance their cause by protest and constitutional challenges. This has blinded us to the different path followed by Japanese Americans. Their constitutional challenge ended in utter failure – the doctrine of “military necessity” found in Korematsu is still the law of the land. And, for the most part, they did not protest. Yet many of them volunteered for the Army, many more were drafted, and it was their heroism in battle that convinced the Roosevelt Administration to free their families at home.

The Sun: What do you want readers to take away from your book?

Asahina: Most of all, an understanding that there is no such thing as “military necessity.” Even in wartime, decisions require trade-offs. “Relocating” 110,000 Japanese Americans from the West Coast struck many people then – and still strikes many people today, sad to say – as a simple, obvious precaution. But it came at a great cost, and not just to the lives of those involved. It cost huge amounts of money and tied up troops and supplies that could have helped end the war sooner – without demonstrably making the country any safer. The same kind of thinking creeps into discussions today. What put an end to this kind of dangerous magical thinking – that there is a simple fix to the problem of homeland security – was the heroism of a determined band of brave soldiers, acting not as protesters and not even as Japanese Americans, but as “just Americans.”