Not long ago, the U.S. was the only country in the world with aircraft that could stroll the skies without fear of being caught. Not any more. Today, militaries from around the world — including Russia and China — are developing their own stealth arsenals. The American monopoly on near-invisible flight is being eroded.

Stealth technology makes vehicles sneakier by limiting the signatures that give them away to enemy radar, sensors and ears. To reduce a plane's radar cross section, designers have two basic options: shape an aircraft to cast incoming radar away from its originating source and coat it to absorb radar waves. Smooth curves and angled edges used to redirect radar waves have become the telltale features of stealth design ever since. Aircraft features on stealth planes have been reshaped, or in some cases, hidden inside a plane in order to avoid bulky, reflective features. Engine exhaust is cooled in order to reduce infrared signatures. Designers have also developed an array of coatings and composite materials to help soak up radar waves and dampen heat.

Since the U.S. rolled out its first stealth fighter, the F-117 Nighthawk, stealth technology has evolved and been adapted for everything from helicopters to drones and even ships. It helped American forces take out Osama bin Laden and level Iraq. The question is how much longer will the U.S. continue to enjoy the advantage of being unseen.

Photo: Department of Defense/Flickr