One veteran interviewed by Rigg was a religious Jew, now 82 and living in northern Germany, who assumed a non-Jewish identity, became an army captain, married a Jewish girl from his hometown and successfully remained a practicing Jew within the German army for the entire war.

Helmut Schmidt, West Germany’s chancellor from 1974 to 1982, told Rigg he successfully hid the fact that he had a Jewish grandfather from fellow officers in the wartime Luftwaffe, the air force. Schmidt thought his case was rare. It wasn’t, says Rigg.

“Thousands of men of Jewish ancestry fought in the Nazi military because they were drafted. But many were career soldiers, and that forced them to apply for the German blood declaration,” Rigg said. “What’s sick here is that, even though Hitler gave the approvals, the officers’ relatives were being exterminated behind their backs. . . . Were most of these people so egotistical they didn’t care who died just so they could live?”

The Nazi regime reeked of hypocrisy, Rigg’s new research makes plain. He documents the case of Field Marshal Erhard Milch, deputy to Luftwaffe chief Hermann Goering. Long rumored to have been Jewish, Milch in fact had a Jewish father, which, according to Nazi code, made him unacceptable to serve in the armed forces. But in 1935, Rigg’s research shows, Goering, Hitler’s chosen successor, falsified documents to declare Milch of Aryan descent by asserting that his mother’s brother was really his father.

About 100,000 Jews served in the German army in World War I, and about 12,000 of them were killed. Veterans thought their service would protect them against the Nazi crackdown early in World War II, Rigg said.