The Watchkeeper WK450 is based on the Elbit Hermes 450 UAV. 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.