History: Despite similar appearances Westland Sea King and Sikorsky S-61 are very differnt helicopters with numerous changes including engines abd British avionics and ASW systems, including search radar, dunking sonar, and processing equipment. The first flight was on May 7 1969.

Initial production was of the HAS.1 -56 of which were delivered to the Royal Navy followed by 21 improved HAS.2 with uprated engines, six blade tail rotors and air intake deflectors/filters. From 1980 Sea King HAS.5 were built with a Sea Searcher radar and ESM while the final version the HAS.6 (six new and 69 concersions from 1990) feature improved processing and ESM. Export equivalent of the Sea King HAS.5 include Sea Kings Mk 41, 42, 42A, 43, 43A, 45 (Pakistani version), 47, 48, and 50. Potentially the most important is the Mk 42B ordered by the Indian navy in the ASW role, for this is based on Westland's Advanced Sea King concept with composite main rotor blades, uprated transmission, strengthened airframe, GEC avionics and porvision for Sea Eagle anti-ship missile.

Search and Rescue Sea Kings are used by Germany, Belguim and Norway and include HAR.5, HAR.3 and HAR.3A.

Operational Service with PN: Pakistan placed its order for Six ASW Sea Kings in December 1972 for the then available Mk 45 version of the helicopter. The 1971 war with India had demonstrated a major shortfall in in ASW capability and this prompted the formation of a seperate naval aviation element. Among the first priorities of the new force was the procurement of effective ASW helicopters.

In October 1974 a team of two former Army pilots along with two ASW observers, five air engineering officers and several underwater controllers, commenced training with Royal Navy Flying Training Unit at RNAS Culdros. Once the Operational and Advanced Flying Phases were completed in 1975, the six helicopters made their way to Pakistan. The first PN Mk 45 flew on 30 August 1974, and deliveries took place between October 1975 and November 1977. The aircraft were delivered by sea after being crated at RNAY Wroughton. The Sea King Mk 45s were broadly equivalent to the Royal Navy HAS.Mk 1 and the Indian Mk 42 versions, with the same MEL ARI 5995 radar, Plessey Type 195M sonar, a Dowty D403M standby UHF radio and an MEL ARI.5954 I-band transponder, but with a General Instrument ALR-606 RWR.

Initially, flying was restricted to continuation training but by 1977, the No. 111 Squadron was fully operational at PNS Mehran. Earlier, the Sea Kings could only perform anti-submarine warfare, however the helicopters were made capable of anti-shipping roles as well. Five of the Pakistani aircraft were modified for a secondary ASV role with provision for the Aerospatiale AM39 Exocet ASM. Initial dropping trials were carried out on the targets at Larkhill by 4515, which had its serial, British civil registration and Pakistani national insignia airbrushed out in many Westland photos, but retained its huge NAVY titles in white and the characteristic white-painted radome. The same aircraft went on to conduct live firing trials at St Raphael (and/or Cazaux, according to some sources) during April to June 1976 and June to October 1977. PN Sea Kings can carry up to four Mk. 46 torpedoes or a pair of AM 39 Exocet anti-ship missiles with a range of 50 km (27 miles), ideal for sea denial roles for these shore-based choppers.

In February 1986, a Sea King had to ditch at sea. One single Royal Navy HAS.Mk 5 was withdrawn from service and converted to Mk 45A standards to act as an attrition replacement for the lost Sea King. This aircraft (originally ZE421) first flew in its new configuration on 17 December 1988 with a new serial ZG935, prior to adapting its eventual Pakistani identity as 4516. It was shipped via Tilbury on 11 January 1989. It was believed to be the only Pakistani Sea King not compatible with the AM39 Exocet anti-ship missile however it might have been made compatible later. The lessons learned from this accident led to the building of a Pakistan Navy Underwater Escape Trainer (PNUET) at PNS Mehran. It was inaugurated on July 9, 1997. It now offers Pakistan's Naval Air Arm aircrew undergoing escape training every six months.

On 29 June 1993, a contract was awarded for installation of a dipping sonar in the Sea King fleet of Pakistan Navy. First flight of an upgraded machine took place in May 1995 with deliveries of the first helicopter starting in July of that year and sixth and final aircraft to be completed and delivered in September 1996. Programme consisted of design and manufacture of installation kits for GEC Avionics AQS-928G acoustic processor and the Plessey Type 2069 dipping sonar. It is basically the Plessey 195 sonar with digital processing which greatly improves deep water capabilit. Kit design and manufacture took place at Fairoaks Airport (UK), with the installation taking place at PN Base Mehran.

Today the aircraft equip No. 111 Squadron the 'Sharks' at the shore-based naval base PNS Mehran at Shahrae Faisal, along with army and air force flying units. The Sea Kings can also operate from the navy's destroyer and frigates, although they seldom operate from the Type 21 frigates which have their own Lynx ASW helicopters.