About 350 people came together on Sunday for a rare glimpse into the sometimes opulent, sometimes shadowy past of the Byron Hot Springs, also known as the top-secret World War II prisoner interrogation center called Camp Tracy.

The occasion was a visit to the former resort by Army Maj. Alex Corbin, author of the book “The History of Camp Tracy: Japanese WWII POWs and the Future of Interrogation.” The guest of the East Contra Costa Historical Society (ECCHS) and the Tracy Historical Society, Corbin reveals how the former resort, whose natural sulfur springs and mud baths attracted celebrities such as Clark Gable, Charlie Chaplin and Mae West in the 1930s, was put to another use in the 1940s: gently wresting military secrets from Japanese soldiers and sailors in an operation so secret that its existence was virtually unknown until just a couple years ago.

Corbin, a military intelligence officer whose duties have included helping to clean up Iraq’s Abu Ghraib prison following the 2004 prisoner abuse scandal, discovered the existence of the Camp Tracy operation while doing research for his master’s thesis. Painstaking research through declassified materials and a nationwide hunt for former soldiers stationed there uncovered the fact that, unlike the harsh coercive tactics used in Iraq, the work at Camp Tracy utilized kindness, friendliness and cultural understanding to glean important information about Japanese morale, ship armaments and military installations.

“Threats and physical coercion were not necessary,” Corbin told the crowd gathered in the rubble-strewn lobby and peering down from the second-floor balcony. “Courtesy and kindness overcame the most reticent prisoner.”

Also on hand was 94-year-old former Lt. Al Nipkow of Walnut Creek, an interrogator at Camp Tracy. “This is very traumatic for me,” he said. “It’s been 70 years since I served here, and to come back to this shell is unbelievable.”

Nipkow said he was never given specific orders to keep the camp’s operation a secret; knowing it was top secret was enough to make those who worked there “clam up.” Some of the eight living Camp Tracy veterans, in fact, were still reluctant at first to talk about their experience, Corbin said.

When they did start talking, they spoke of their admiration for the Nisei, American-born descendents of Japanese immigrants who worked hand-in-hand with their Caucasian counterparts to question the POWs. Corbin said many of the Nisei worked while their families languished in internment camps, yet still did their duty to their country.

The camp’s innovative tactics included the preparation of “home-cooked” meals by Japanese chefs, allowing POWs to use the resorts spas and mud baths, and placing electronic eavesdropping devices throughout the building while housing prisoners two to a room (sometimes with a Nisei pretending to be a prisoner) to encourage conversation, which was then recorded.

Corbin said he is sometimes asked if the Camp Tracy tactics would have worked in Iraq.

“My thoughts are that if you start off at (a severity of) one, you can always ramp up,” he said, noting that his thoughts were his own, not necessarily those of the Army. “But if you start at 10, you can’t expect to start getting nicer and expect to get information. I think (the Camp Tracy methodology) would really help a lot in our current endeavors.”

The event’s hostess was historian Carol Jensen, an expert on Byron Hot Springs, who conducted tours of the building and grounds. The ECCHS garnered nearly 50 family memberships, something Jensen said showed the keen interest that abounds in far East County history. The Hot Springs, which are fenced off most of the time, will “most definitely” be the scene of another such event in the future.

As for that future, the current owner of the Hot Springs, Dave Fowler, was on hand at a meet-and-greet event at Byron’s Wild Idol following the event. He’s developed plans to rebuild the original hotel and return the site to its previous splendor. The project, however, is currently stalled at the county level, seeking permits.