The Watchkeeper WK450 is based on the Elbit Hermes 450UAV. The engine is a rotary Wankel engine. It has a mass of 450 kg and a payload capacity of 150 kg, with a typical endurance of 17 hours. It was originally intended to enter service in June 2010. The Watchkeeper is built in the UK by a joint venture company, UAV Tactical Systems (U-TacS), set up by the Israeli company Elbit Systems (51% ownership) and French company Thales. UAV Engines Ltd, who build the rotary engine in the UK, is a wholly owned subsidiary of Elbit Systems. The majority Israeli ownership has caused some unexpected problems obtaining U.S. export authorisation for some components.
On 15 July 2007, the UKMoD revealed that 54 Watchkeepers will be delivered to the British Army. The average cost to the taxpayer is therefore £800m divided by 54 aircraft, approximately £15m per platform. However, this figure includes construction of new basing facilities at Boscombe Down airfield, ground training facilities and simulators at the School of Artillery, Viking armoured vehicles and other equipment for tactical parties, ground control stations, development and testing of extensive aircraft modifications including automatic take-off and landing and the integration and provision of new sensors including radars.
Watchkeeper's first UK flight took place on Wednesday 14 April 2010 from ParcAberporth in Wales.
In October 2010, the contract was extended by a further 18 months, and the delivery date slipped. Deployment by the Royal Artillery is said to be imminent in 2013, though certification by the Military Aviation Authority is still awaited. As of 2013, the programme is running about three years late; in September, release to service approval was expected to be granted before the end of the year. British Army officials say the Watchkeeper could enter service in spring 2014. As of January 2014, 26 air vehicles have been produced with another 28 on order, and 14 ground control stations have been produced with one more on order. Watchkeeper aircraft have performed over 600 flights totaling 950 flight hours. The Watchkeeper system will be in service with the British Army until 2040.
The Royal Artillery has a future aspiration to weaponise Watchkeeper.