The Merlin HM Mk 1 has been in Service with the Royal Navy since 1998. There are 5 Squadrons, 814 Sqn, 820 Sqn, 829 Sqn, 824 Sqn and 700 Sqn and all are based at the Royal Naval Air Station Culdrose in Cornwall when disembarked. Primarily employed as an anti-submarine helicopter and equipped with sonics and sonar systems the aircraft also contributes to anti surface warfare.

Merlin is designed to operate from both large and small ships' flight decks, in severe weather and high sea states, by day and night. When embarked the aircraft operates primarily from the Auxiliary Oiler (Replenishment), Carrier and Type 23 Frigate but can also embark in other platforms with a capable flight deck. A high level of reliability, serviceability and ease of maintenance are a pre-requisite. The aircraft is therefore configured both structurally and in terms of mission system and cockpit design, to meet the demands of the harsh maritime environment.

Powered by three Rolls Royce Turbomeca gas turbines, the rugged, crashworthy airframe is of modular construction, mainly of aluminiumlithium, aluminium and composites. The rotor system, which is fully folding, benefits from some of the most advanced helicopter aerodynamics in the world. With a maximum all-up-mass of 14,600 kg, and a top speed of 167 kts, the Merlin can carry four homing torpedoes or depth charges, and has sufficient fuel for a radius of operation of over 200 nautical miles.

The aircraft and its mission system are managed by two computers, linked by dual data buses. All crew stations can access the management computers and can operate the tactical displays, fed by the Blue Kestrel radar. Navigation is state of the art with ring laser gyros, inertial reference systems GPS, doppler and radar altimeters. Electronic Support measures (ESM), are supplied by the new Orange Reaper and the mission system is completed by a comprehensive communications fit that includes datalink.

To date the aircraft has contributed to many operations and exercises, throughout the world including hostilities in the Northern Gulf in 2003.