Editor's note: Nathaniel Frank is author of "Unfriendly Fire: How the Gay Ban Undermines the Military and Weakens America" and is senior research fellow at the Palm Center, a think tank at the University of California, Santa Barbara, that has focused on gender, sexuality and the military. He also teaches on the adjunct faculty at New York University.

Nathaniel Frank says there's no evidence that letting gays serve openly would harm the military.

(CNN) --   This week, four senior retired officers wrote an op-ed in The Washington Post predicting "grave harm" to the military if President Obama moves forward with his vow to let gays serve openly.

"Our experience," they wrote, "and that of more than 1,000 retired flag and general officers," suggest that lifting the ban would harm unit cohesion, recruitment and retention, and would ultimately "break the All-Volunteer Force."

The argument is an old one, and was an effective canard in defeating President Clinton's move to lift the ban in 1993. But it has never been rooted in fact or evidence, and the effort of these officers to defeat equal treatment this time around will face mountains of opposing data and a dramatically changed cultural landscape.

The officers who oppose openly gay service do not base their arguments on any new information. In addition to their own experience -- an impressive credential that's nevertheless too vague to hang an argument on -- the officers rely on a single poll.

They cite an unscientific survey -- it does not draw from a representative sampling but from newspaper subscribers -- indicating that 58 percent of the military oppose lifting the ban and that, if it's lifted, 24 percent claim they will leave or consider leaving after their tour ends.

But it's naïve at best, and disingenuous at worst, to confuse this opinion survey with a sound prediction of actual behavior. When both Britain and Canada proposed lifting their gay bans in the 1990s, similar opinion surveys found much higher numbers -- about two-thirds in both cases -- claiming they, too, would leave. In each case, no more than three departures were attributed to the policy change. Three.

In fact, the evidence showing that openly gay service works is overwhelming. Since 1957, when the U.S. military began doing its own studies on gays in the military, every last bit of research has shown that openly gay service works.

Studies of foreign militaries include a 1993 Government Accountability Office study of allied nations that found that "the presence of homosexuals in the military is not an issue and has not created problems in the functioning of military units"; a 1994 assessment by the U.S. Army Research Institute for the Behavioral and Social Sciences finding that predicted negative consequences of ending gay exclusion in the Canadian Forces never materialized; the 2000 assessment of the British Ministry of Defense, calling its new policy of equal treatment "a solid achievement" with "no discernible impact" on recruitment or other critical variables; and four academic studies conducted by the Palm Center, where I work, finding that lifting bans in Britain, Israel, Canada and Australia had no negative impact on military readiness, including on recruitment and retention.

The officers writing in The Washington Post question the relevance of foreign militaries to this debate, mocking the idea that the U.S. military "must emulate Denmark, the Netherlands and Canada." But they failed to note that 24 of our closest allies let gays serve openly, including Britain, whose combat-tested soldiers and sailors serve shoulder to shoulder with U.S. forces.

While our military and culture are unique in the world, it's an astonishing vote of no-confidence in American troops to say that they are not capable of doing what 24 other militaries have done successfully. Ours is a professional, disciplined fighting force, and the assertion that a diverse military would lack order and discipline is, as Rep. Patrick Murphy, an Iraq War veteran, has said, "an insult" to him and the entire U.S. military.

But it's not just foreign militaries that provide real evidence on gay service. A majority of U.S. troops
Who oppose letting gay troops serve? who are accepted widely today in military?
58 percent of the military gays
question: Who oppose letting gay troops serve?, answer: 58 percent of the military | question: who are accepted widely today in military?, answer: gays