TULELAKE, Calif. — Under a cloud-filled sky, the Japanese-American pilgrims sat on folding chairs facing a vast, flat and dusty landscape whose monotony was broken only by two oddly shaped mountains that rose to the east and west. For the souls of the hundreds buried in a long-vanished cemetery here, a Buddhist minister offered prayers and rang a bell, though its invocation was almost lost as a propeller plane took off from a nearby airfield.

Nearly 400 Japanese-Americans journeyed from June 30 to July 3 to this remote corner of California, where 18,789 people of Japanese ancestry were incarcerated during World War II. The turnout was one of the highest ever for the four-day pilgrimage, which occurs every other year around the Fourth of July, organizers said. They surmise that as the number of the camp’s survivors dwindles, there is a growing urgency to understand — and reinterpret — what has been a hidden subchapter in America’s history.

Of the 10 internment camps in which about 120,000 Japanese-Americans were confined during the war, it was Tule Lake that held those branded “disloyal,” the ones who answered “no” to two critical questions in a loyalty test administered by the federal government....