(Courtesy of BookFinder.com) (Courtesy of BookFinder.com)

Military incompetence has lost wars and brought down empires. And now it’s toppled the reign of Madonna.

For the first time since 2010, the pop singer’s soft-porn photo book “Sex” is not the No. 1 most searched-for out-of-print book in America.

That honor now belongs to Norman F. Dixon’s “On the Psychology of Military Incompetence” (Basic, 1976). Dixon is a professor emeritus of Psychology at University College London. (He has posted no photos of himself in spandex.) An e-copy of his history of snafus from the Crimean War through WWII is readily available, and new paperback copies can be special ordered from the UK. But if you’re an American more interested in scrambled battle plans than tangled underwear models, you’ll have to turn to the used book market.

In fact, Madonna’s decline is even more dramatic.

“Sex” has fallen all the way to No. 3, giving up the No. 2 spot to the always arousing “Lovely Reed: An Enthusiast’s Guide to Building Bamboo Fly ” by Jack Howell (Pruett, 1998). Pristine hardback copies are currently for sale for more than $500, although cheaper copies can be found for as little as $50.

Fish over sex? This may be the best evidence yet of the graying of America. (Will we stoop to a tasteless pun on the word “rod”? We will not.) But even at No. 3, Madonna’s metal-clad, spiral-bound “Sex” still commands far higher prices than the books above it on the list. Signed, like-a-virgin copies fetch as much as $750.

The remainder of the top 10 list offers an equally weird collection: Stephen King novels, children’s stories, a defense of God and “The Collector’s Guide to Colt .45 Service Pistols.”

The new annual list of top 100 most searched-for out-of-print books was released today by Bookfinder, which has been tracking the data for more than a decade.