Adm. Gary Roughead, the Navy's top officer, is all about practicality these days. In a document he issued to his sailors earlier this week, he vowed that when it came to military gadgets, the Navy would "only develop those capabilities we need, not just want." In these tough economic times, Roughead speaks for a lot of the military's top brass. Except when he doesn't. R&D in the American military -- and other militaries, ally and enemy alike -- is a story of madcap engineering, oddball design, and loose definitions of "need" and "want." Think rocket launchers that shoot nukes, flying saucers and laser-blasting jets. Definitely laser-blasting jets. We take a look at some of the crazier guns and vehicles to make it to the prototype stage, here and abroad. Sure, the admirals and generals say they're being practical. But we all know they can't resist a good WTF weapon. Grenade-Shooting Robo-Scout Imagine seeing this rolling through your cul-de-sac. In 1993, the Marines figured they needed an unmanned scout to gather intel in hostile territory. By 2005, Carnegie Mellon University got a $26 million contract to design the Gladiator tactical unmanned ground vehicle -- a tube-heavy remote-controlled robo-scout, tricked out with a grenade-launching system, smoke cover and chemical-weapons detection. Photo courtesy of the U.S. Department of Defense

Canadian Spy Saucer Another reason to love Canada. In the 1950s, our neighbors to the north helped us develop the Avro-Car as a Cold War vessel for reconnaissance missions during a vertical-take-off-and-land engineering craze. The silver saucer was a mere 8 feet in diameter and seated two at most, staying aloft thanks to a 5-foot fan on the bottom powered by three gas engines. The noise made by the fan made it a poor stealth choice, and it couldn't rise higher than five feet without losing stability. By 1960, the Frisbee-like vertical take-off-and-land craft had run through $10 million in research money and the next year, the company producing it went bankrupt.

Suicidal Nuclear Bazooka What can stop Soviet tanks from plowing westward across the German plain? If it was the late 1950s, one answer was a small nuclear warhead fired from a recoil-free rifle. The M-28/M-29 "Davy Crockett" lobbed a 76-pound nuke with a yield smaller than a kiloton (think 10 tons of TNT) between two-and-a-half and four miles, depending on the size of the gun. Problem was, the warhead would detonate at a minimum of 1,000 feet from launch, sending a potentially fatal dose of radiation back at U.S. troops. (Also, the rifle wasn't so recoil-less.) Tested only twice in 1962, it took until 1971 to get rid of the Davy, but it achieved immortality as the Nuclear Bazooka in Starship Troopers. Photo courtesy of Wikimedia

Headless Obedient Robot Pack Mule You don't have to feed it and it doesn't mind being kicked -- it just gets back up and goes on its way. Just load Boston Dynamics' BigDog robot with up to 300 pounds gear and program it to get to Point B, through rugged terrain and uphill. But Darpa, the BigDog's ultimate master, is a disciplinarian: In 2008, it said it wanted the robotic mule to lug up to 400 pounds and become independent of joystick controls, relying on GPS and sensors to follow troops around. But it's still going, although it may become too pricey to take home from the pound. And isn't it creepy that this thing has no head?

Unacknowledged, Unwanted, Star Wars-esque Stealth Ship It looks like leisure-time headgear for Darth Vader. But you're not supposed to see the Navy's Sea Shadow, let alone make fun of it: This 164-foot Darpa-funded stealth ship was supposed to evade radar detection. It was used for some secret missions in the '80s and '90s, but never actually given the U.S.S. designation, and it stayed shoreside in San Diego between 1993 and 2006 before decommissioning. Sadly, museums don't even want it, raising questions about the power of the Dark Side. Photo: U.S. Navy

Soviet Nuke-Proof Tank Why, yes, that is a tank with a flat, rounded hull that you see. In the 1950s, the Soviet Union didn't just want a 60-ton tank that could fight on uneven terrain. It wanted a heavy tank that wouldn't flip over in the event of a nearby nuclear detonation. Why the Obyekt 279's shape would stand up to a nuclear shockwave is unclear, but in 1960 it became a moot point. The Red Army decided no tank should exceed 50 tons, and the 279 was mothballed before it could face so much as a 1-kiloton nuclear exchange.

Missile-Zapping Flying Lightsaber The crown jewel of the Missile Defense Agency and a favorite on Capitol Hill, the Airborne Laser is a reconfigured Boeing 767 that carries what looks like a disco ball on its nosecone. But the disco ball fires a powerful laser, meant to disable an incoming missile, either in flight or as it takes off. Alas, the thing has been a $4 billion sinkhole, even though Congress keeps throwing money at it. In September, it couldn't shoot down a dummy missile, even though the laser hit its target. General Norton Schwartz, the Air Force chief of staff, told dismayed legislators that the Flying Lightsaber "does not reflect something that is operationally viable." But whether that'll be enough to kill the oft-resurrected laser for good remains to be seen.

Disco-Dazzling Light Gun Someone at the Air Force Research Laboratory's Directed Energy Directorate in 2005 read too many Rob Liefeld comics before designing this massive light-shooting toy. The Personnel Halting and Stimulation Response rifle, or PHaSR, won't kill you. It'll just shoot you with two low­-power diode­-pumped lasers to "dazzle" you into disorientation and temporarily blind you. Although the Air Force pledged to equip it with an "eye­-safe laser range finder" so it wouldn't permanently put someone's eye out, the military soured on PhaSR by 2008. But now it's in development by the National Institute of Justice, the R&D arm of the nation's police. So why don't you do what the officer says? Photo: Wikimedia

Ginormous, Missile-Toting Russian Helo This '60s-era Russian helicopter was the largest ever built, possessing a 220-foot wingspan that gave it longer reach than the wings of a 747 and no tail rotor. It weighed in at over 231,000 pounds. And in 1969, the V-12 broke a world record by climbing to 7,000 feet while carrying more than 44,000 pounds. Why so huge? Because the Soviets intended it to be the world's only helicopter that carried a ballistic missile -- without ever asking why they'd want a missile-equipped helo. By the mid-'70s, they stopped development, even after the V-12 wowed at the 1971 Paris Air Show.