Aboard the USS George H.W. Bush - A bat-winged experimental Navy drone executed landings on an aircraft carrier for the first time Wednesday, marking a major advance in robotic aviation.

A flat gray drone that resembles a giant stingray without a tail, the X-47B glided smoothly onto the flight deck of the USS George H.W. Bush about 80 miles off the coast of Virginia. The drone had demonstrated it could take off from a carrier during testing in May, but the landing was considered the most difficult obstacle to surmount given the confined space on the ship and unpredictable conditions at sea.

Navy leaders hailed the event as a milestone in aviation, the culmination of an eight-year, $1.4 billion program to test the feasibility of basing long-range drones on aircraft carriers. "What you saw here is the first of the next generation of naval aircraft and the amazing capabilities it will give us," said Navy Secretary Ray Mabus, speaking to reporters on the ship.

The U.S. military has been flying drones in combat zones for about 15 years, and unmanned aircraft have taken on an increasingly vital role in warfare. In addition to meeting the challenge of landing on a large ship, however, Wednesday's flight marked the first time that a military drone flew autonomously for an extended stretch of time, without any human direction.

Other large drones, such as the Predator and Reaper unmanned aircraft flown by the Air Force and CIA, require a human pilot to operate the plane remotely with a joystick, issuing electronic commands over a satellite link. While the X-47B still followed a flight path scripted by personnel on the ground, it executed the landing entirely on its own, calculating by itself how fast to approach the ship and precisely when to put its wheels down.

The drone took off about noon from Patuxent Naval Air Station in southern Maryland and flew about 140 miles to the George H.W. Bush. On its first approach, the ship's crew waved off the plane as part of a planned test, then ordered it to circle around and try again. It did so flawlessly and caught the third wire on the flight deck as it landed, similar to the procedure for a regular fighter jet.

Although Navy officials hailed the landing test as a success, it will take several more years before drones will operate normally on aircraft carriers. The X-47B-X stands for experimental-was intended merely to demonstrate the feasibility of landing on a ship. Two of the drones, built by Northrop Grumman, will be retired by the end of the year and sent to museums.

The Navy is currently soliciting contracts to design and build new carrier drones, but expects that it will take until 2019 to field them.

The Navy already flies drone helicopters - known as Fire Scouts - from ships, although these aircraft have limited range and capabilities.

Navy officials said the new generation of carrier drones will probably be used predominantly for surveillance, as well as to refuel other aircraft. They will also likely be able to carry missiles and stay airborne for up to 30 hours - three or four times longer than manned planes. It is envisioned that the drones could be converted into stealth aircraft to avoid enemy detection, yet the Navy insists that is not an immediate priority.

While officials described the drones as revolutionary, Adm. Jonathan Greenert, the chief of naval operations, said they would not replace the need for manned aircraft and would represent just one component of a carrier's air wing.

And despite the allure of the new technology, Greenert said the Navy was already on guard against cost overruns and delays that frequently plague other military weapons programs.

"We've got to bring this thing in by the end of the decade," he said in an interview. "There will not be a lot of patience for programs that run over cost and past time."