The Thales Watchkeeper WK450 is an unmanned aerial vehicle (UAV) for intelligence, surveillance, target acquisition, and reconnaissance (ISTAR) used by the British Army.

[6] It was originally intended to enter service in June 2010,[7] but years of delays, technical issues, hardware modifications, difficulties in training sufficient pilots and incidents means that it was not expected to be fully operational until late 2018.

A prime difference between the Hermes 450 operated by the British Army and Watchkeeper was that the H450 was fitted only with an electro-optical/infrared sensor, while the WK450 has in addition a dual-mode synthetic aperture radar and ground moving target indication system that allows it to see through all weather conditions.

[15] The next phase of the program was initiated to support an operational need, which was identified at the start of the War in Afghanistan, to provide the UK Armed Forces with all-weather day and night surveillance capability.

In February 2003, the Ministry of Defence announced that two contenders reached the final stage of the tender, a group that includes Thales (at the time still operating under the name Racal Electronics) and Elbit Systems,[16] and a second contender Northrop Grumman, after BAE Systems and Lockheed Martin were deselected (BAE subsequently entered negotiations to join forces with Northrop for the bid).

[21] In June 2007, the joint venture company UAV Tactical Systems, was awarded a $110 million contract to provide an urgent intelligence, surveillance, target acquisition and reconnaissance support capability for the British Army, in Iraq and Afghanistan, using Hermes 450 UAVs leased from Elbit systems (and not using any Watchkeeper WK450, that was still in development).

[25] Watchkeeper's first UK flight took place on Wednesday 14 April 2010 from ParcAberporth in Wales,[26] but due to numerous delays the delivery date slipped.

[2] A report by the Major Projects Authority, published in June 2015, revealed that the estimated cost of achieving full operational capability of the program is £1.2bn.

[14] In June 2023, Defence minister James Cartlidge stated that the Watchkeeper program had cost £1.35 billion to date, including necessary airfield upgrades at Aberporth and Boscombe Down.

[35] In November 2024, Defence Secretary John Healey announced to the UK House of Commons that some military equipment, including the entire fleet of Watchkeeper WK450 Mk1 drones, would be retired earlier than planned to cut costs.

This was due to an avionics power failure and the air vehicle being unable to regain communication with the ground control system.

The aircraft were stationed at Camp Bastion to provide force protection for British troops and worked alongside Hermes 450s that it is derived from.

It cued a Hermes 450 onto a target for continued tracking, which then passed the information on to a Royal Air Force MQ-9 Reaper to conduct an airstrike.