As many as 300 times a week, Waterman receives an e-mail message: Someone—a co-worker or an employee, a boyfriend or ex-husband, a guy in a bar—has bragged that he was a Navy SEAL, generally during the Vietnam war.

Was he lying?

Waterman goes to the computer at his home on Maine’s coast. With a few mouse clicks and key strokes, he checks to see if the alleged SEAL can be found in a database listing all 9,600 graduates of the underwater demolition course that SEALs must complete to wear the trident of the elite Sea-Air-Land force.

In some cases the names match; the individual was a SEAL. But far more often it turns out that he is a wannabe who is posing as a SEAL to try to enhance his reputation.

"These guys are slime," Waterman says.

On average, the 55-year-old Waterman—a lobsterman, photographer, commercial diver, and computer consultant—devotes an hour a day to unmasking bogus SEALs. The U.S. government does not do similar work.

"Other folks out there feel very passionately about this issue," says Lt. Cmdr. Darryn James, a spokesman for the Special Warfare Command in San Diego, Calif. "We don’t have any position one way or the other on what they are doing."

Waterman acknowledges that many wonder why he does it. "Some say, ‘Why don’t you guys get a life and leave these people alone. Who cares?’ That’s one attitude," he said.

But there are others, he says, who feel that it’s "about time somebody exposed these people for what they are." And there are veterans who view these counterfeits as an affront to the memory of fellow SEALs who were killed and wounded during the war.

Two years ago, Waterman and some of his SEAL buddies traveled to Massachusetts with a BBC crew in tow and knocked on the door of a man who claimed to be a Vietnam-era SEAL who had won the Navy Cross and received three Purple Hearts. After being dressed down, the man vowed never again to lie about his military record.

But mostly, Waterman just posts the names of "outed" fake SEALs on the Internet on a "Wall of Shame" that spells out their transgressions. A one-star rating goes to "keyboard commandos" who make anonymous claims online. The worst offenders, who are given five stars, are those who lie for personal gain, in some cases to burnish a campaign for public office.

Some entries offer comments: "Incorrigible." "Apologized." "Makes claims to all who will listen." "Still at it, now has shaved his head. Guess he was too well known from his photos here."

There is also a section that attempts to answer the question of whether Minnesota Gov. Jesse Ventura was in fact a SEAL. (Yes, the website says.)

Waterman is not a former SEAL, but he served in Vietnam as a photographer with Underwater Demolition Team 13, and underwent much the same training as the SEALs. He is the only non-SEAL among the small group of Navy veterans who has access to the SEAL database.

Although there were only 200 SEALs in Vietnam while he was there, Waterman said the number of pretenders runs into the thousands.

"Most of these people were the innocuous beer hall Rambos, who were just blowing hot air," he said. But he said they also include three college professors, four or five doctors, and a surprisingly large number of ministers.

The number of inquiries Waterman has received has grown from a trickle to a flood after a handful of high-profile cases focused attention on false claims about combat duty in Vietnam.

The most widely publicized was that of Pulitzer Prize-winning historian Joseph Ellis, who claimed to have been a platoon leader with the Army’s 101st Airborne when he actually was an instructor at West Point.

Waterman said those kinds of lies have become commonplace. Some fakes claim to have been Medal of Honor recipients or to have been prisoners of war; lies about wartime resumes often revolve around elite units like Army Special Forces, reconnaissance teams, and SEALs.

James, the Navy lieutenant commander, could not estimate the number of fake SEALs. The high esteem in which the SEALs are held, he said, might prompt some people to inflate a lesser or nonexistent military resume.

"They’re considered the best of the best. So, perhaps, that is why some people would want to identify with them," he says.

Fabricated accounts of wartime exploits are nothing new, he says, but until now it was difficult to detect the phonies.