It scours the bottom of Navy ships, invades the crevices of Air Force jets and costs the Defense Department $23 billion a year. It’s not a clandestine agent or biological weapon. In fact, it’s in your home right now.

It’s rust.

Apparently, rust is pretty expensive (and ugly). Fighting corrosion costs over 3 percent of the national GDP, or about $1,000 per person per year. The Defense Department estimates that it will spend $114.5 billion over the next five years on the nasty nuisance.

It’s a problem because corrosion happens to anything exposed to weather — old things in particular. Which means that all those Cold War-era jets, tankers and bombers are hit especially hard. For the bulk of this ancient fleet – built before any of its current pilots were even born – that corrosion is only getting worse. Since the Pentagon and Congress haven’t gotten their act together to replace these clunkers, they – and the rust – may stick around for a while.

Even new planes aren’t safe; leaky F-22’s are expected to cost the Air Force millions. And rust is a constant problem for the Navy, since it has a notoriously hard time avoiding salt water.

So how do we deal with all this metallic decay? The Defense Department Corrosion Office has some ideas. Set up in 2003, the aptly named CorrDefense agency is all-out dedicated to hunt down rust wherever it may appear. If you’re not feeling quite so passionate about the endeavor, this inspirational video by enthused rust-buster Daniel Dunmire might get you fired up.

Otherwise, the U.S. Navy’s Mega Rust 2011 conference is sure to stir up some anti-corrosion sentiment. This annual get-together of military personnel, government officials, researchers, manufacturers and suppliers seeks to advance the decorrosifying agenda.

Technically, the problem is bigger than just rust. Rust is only the most commonly known type of corrosion, and occurs when iron reacts with water or moist air. The broader category includes any type of metal broken down or disintegrated by a chemical reaction.

There are all sorts of ways to get a grip on this pesky scourge. Coating surfaces with a paint or spray is a common treatment, but this sort of rust-proofing doesn’t last very long. It’s easy to miss hard to reach places, and those unprotected spots are most prone to damage. Even a tiny chip, crack or peel will start to break down. Without constant maintenance and frequent recoating, rust is inevitable.

While the military is looking into more coating options – from aluminum- to polyurethane-based waterproofing – there are some alternatives. Cathodic protection is an electrochemical process that prevents corrosion entirely, and superfinishing is a surface treatment process that prevents damage from friction.

Combined with better maintenance, new technologies could cut costs by 30 percent over 20 years, Dunmire recently told Bloomberg news.

Until then, with anti-corrosion online training games like Inspect and Protect or Protocol 424, you can fight the insidious menace yourself. Dunmire would be proud.