A stealthy unmanned aircraft system developed by Lockheed Martin's Skunk Works division has secretly joined the US Air Force inventory.

The USAF confirms that the RQ-170 Sentinel is in development, and is expected "to provide reconnaissance and surveillance support to forward-deployed combat forces", according to a statement released on 4 December.

The announcement comes after a series of images of a jet-powered, stealthy aircraft have appeared on the internet since last April, including a clear shot of the aircraft that circulated widely in early December.

But it was not immediately clear whether the aircraft shown in pictures and the RQ-170 are the same. Besides describing the RQ-170 as stealthy, the USAF released no further technical information about its new UAV, or any photos.

Kandahar UAV 
 © Jean-Dominique Merchet
Could this mystery UAV, spotted in Kandahar, be the RQ-170?

The RQ-170 is flown by the 30th Reconnaissance Squadron, a unit reactivated by the USAF at the Tonopah Test Range in California on 1 September 2005, according to a service fact sheet.

In a news release about a change of command, dated 10 August, the USAF described the 30th as a "developmental UAS squadron under the 432nd Wing, Air Combat Command".

The RQ-170 joins the USAF's growing inventory of large surveillance aircraft, which includes the Northrop Grumman RQ-4 Global Hawk and General Atomics Aeronautical Systems RQ-1 Predator/MQ-9 Reaper. But the Sentinel appears to be the first publicly acknowledged operational UAS designed for stealth.

The Sentinel's confirmed existence also sheds new light on Lockheed's activity in the large UAS market, which was previously considered to be undeveloped.

Lockheed's Dark Star unmanned air vehicle lost a competition in the late 1990s to the Global Hawk. Since then, Lockheed unveiled the P175 Polecat, a stealthy, high-altitude UAS, but the only known example crashed during a flight test.

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Source: Flight International