Critics in the US and abroad have charged that drone strikes cause widespread civilian deaths and are conducted with inadequate oversight. Defence analysts say drones are the future of warfare.
The new Joint Strike Fighter jet "might be the last manned fighter the US ever builds. They're so expensive, they're so complex, and you put a human at risk every time it takes off from a carrier", said James Lewis, senior fellow at the Centre for Strategic and International Studies in Washington.
"This is the next generation of military technology the unmanned vehicles, the unmanned submersibles, the unmanned aircraft. This will be the future of warfare, and it will be a warfare that is a little less risky for humans but maybe a little more effective when it comes to delivering weapons and effect."
While the X-47B isn't intended for operational use, it will help navy officials develop future carrier-based drones. Those drones could begin operating by 2020, according to Rear Admiral Mat Winter, the navy's programme executive officer for unmanned aviation and strike weapons.
The X-47B is far bigger than the Predator, has three times the range and can be programmed to carry out missions with no human intervention, the navy said.
While the X-47B isn't a stealth aircraft, it was designed with the low profile of one. That will help in the development of future stealth drones, which would be valuable as the military changes its focus from the Middle East to the Pacific, where a number of countries' air defences are a lot stronger than Afghanistan's.
"Unmanned systems would be the likely choice in a theatre or an environment that was highly defended or dangerous where we wouldn't want to send manned aircraft," Branch said.
During yesterday's flight, the X-47B used a steam catapult to launch, just as traditional navy warplanes do.
The unarmed aircraft then landed at a base in Maryland.
Human Rights Watch said it was troubled by what it described as a trend toward the development of fully autonomous weapons that can choose and fire upon targets with no human intervention.
"We're saying you must have meaningful human control over key battlefield decisions of who lives and who dies. That should not be left up to the weapons system itself," said Steve Goose, director of the arms division at Human Rights Watch.
Developed by Northrop Grumman under a 2007 contract at a cost of US$1.4 billion ($1.7 billion), the X-47B is capable of carrying weapons and providing around-the-clock intelligence, surveillance and targeting, according to the navy.
- AP
