Did interrogators at Byron Hot Springs sometimes use gas masks smeared inside with rancid onions to loosen the tongues of World War II prisoners of war?

That question remains unresolved, but still worth asking, after my visit to Byron Hot Springs on Sunday afternoon.

I was among the more than 300 people who walked through what is left of the venerable spa hotel in a tour and talk that gave people a glimpse of what remains of the ultra-secret prisoner-of-war interrogation center.

The three-story building with full basement, constructed in 1914, has never looked worse in its 96-year history. Although the exterior red brick walls are intact, the interior elements are crumbling, and everything — inside and out — is covered with graffiti.

But regardless of the building’s sad condition, it was still a fascinating place for the visitors to see where Japanese and German prisoners of war were questioned from 1942 to 1945 in an effort to gain valuable wartime intelligence. And valuable information was indeed secured.

As the visitors gathered Sunday in the ground-floor reception area and above around a second-story railing, U.S. Army Maj. Alexander Corbin, author of the recently published book, “The History of Camp Tracy,” spoke.

Corbin stressed that the interrogation techniques used at the base, known as “P.O. Box 651, Tracy, Cal.” or “Camp Tracy,” worked amazingly well to glean valuable information from Japanese POWs. Those techniques included treating the prisoners with respect, putting them at ease, befriending them, feeding them Japanese food prepared by special chefs and using second-generation Nisei interrogators who were fluent in the Japanese language and familiar with cultural issues.

According to Corbin’s book, those techniques contrasted with at least some of the aggressive interrogation techniques, including water-boarding, reportedly used early in the Iraq war at Abu Ghraib in Iraq and Guantanamo Bay, Cuba. That contrast, underscoring the success of Byron Hot Springs methods, is a central theme of Corbin’s book.

After his talk, I asked Corbin about the onion masks, of which I first caught wind in 2001 from an e-mail sent by Willaim Piavis, son of a dentist who was stationed at Byron Hot Springs during the war. Piavis wrote: “I do remember my father telling me one time that they used ‘onion masks’ to gain information from the PWs.”

A year later, when I interviewed Bill Burdette, first sergeant of the Army guard, Bill didn’t bring up the topic — but when I asked about it (to his surprise), he confirmed that onion masks had been used on some POWs while medical personnel stood by, monitoring the pulse and blood pressure of those wearing the masks and laboring to breathe.

Corbin said he had heard the term “onion masks” used vaguely, but he didn’t find any details about their use or confirmation in written interrogation reports. He said his focus in the book was on the interrogation of the Japanese POWs, who comprised the largest number of prisoners at Byron, and not the smaller number of Germans.

If used at all, the onion masks could possibly have been put on the faces of Germans and not Japanese prisoners, he said. And that possibly could be true, although neither the dentist’s son nor Burdette restricted their use to German POWs.

Japanese veterans who had been interrogated at Byron Hot Springs never mentioned onion masks in extensive interviews with Japanese filmmakers who produced an in-depth documentary on the secret base and the valuable information about ships, planes and Japanese homeland targets given up by Japanese POWs.

If Germans were the only targets, then some of the most likely candidates for onion-masks were members of a U-boat crew who were grilled at Camp Tracy about the killing of one crew member they suspected of giving up information to U.S. interrogators at an East Coast base. The U-boat crew was taken to Byron Hot Springs for further, intensive interrogation, which a book about the episode indicated was very aggressive. The U-boat sailors refused to give up any information about the killing, however, and were later executed at Fort Leavenworth, Kan.

The bottom line, for me at least, is that the use of onion masks remains a part of “Camp Tracy” history, whether Corbin included it in his book or not. Perhaps the Army major can learn more about their use, if he pursues the issue in further research. From our brief conversation Sunday, he didn’t seem very anxious to do so. Stay tuned.

• Sam Matthews, Tracy Press publisher emeritus, can be reached at 830-4234 or by e-mail at shm@tracypress.com.