A Magnetic Anomaly Detector(MAD) 'stinger' was added to the tailcone, a search radar was added in the nose, and a fin-tip radome ('football') was fitted to accommodate ESM equipment.
A new ventral weapons pannier was added beneath the cabin, giving a distinctive 'double-bubble' cross-section, these changes necessitating an increase in fin area. In the front of this cabin there is the search radar. The windshield of the cockpit is enlarged.
A searchlight is added in the right wing. The first prototype was powered by the production Nimrod's intended Rolls Royce Spey engines and made its maiden flight on 23rd May 1967, serving as an aerodynamic test-bed and for airframe/engine integration.
The second retained Avons and flew on 31 July, serving as the avionics development aircraft.
The first of 46 production Nimord, the MR.MK1s flew on 28th June 1969, entering service with No.236 OCU in October 1969, eventually equipping five squadrons, one based at RAF Luqa, Malta. The British withdrawal from Malta rendered the last batch of eight Nimrods surplus to requirements, although they could usefully have been used to spread hours more evenly across the fleet, extending the Nimrod's life. Five were delivered to the RAF, and the others were retained by BAe for trials, but their useful life was short, seven of them being selected for conversion to AEW.Mk 3 standards, along with four MR.MK1s. All of these airframes were effectively wasted, since the Nimrod AEW.Mk 3 never entered productive service, defeated by technical problems, and all but one were scrapped (the survivor becoming an instructional airframe).
The MR.MK1 uses 4 RB.168-200 "Spey" turbofan engines, each power 5506kg. The whole fuel capability is up to 38940kg. With the 6 disassembly fueltanks in the cabin, it can be added to 45785kg. There 12 crew onboard, including two pilots and one engineer in the cockpit, navigator, tactical navigator, radio operator, radar operator, two sonar operators, ECM and MAD operator and two surveillance and cargo operator. The sonar system is in the afterbody, includes types of sonar buoys, all loaded on the launchers. The weapons for a single MP.MK1 includes nine torpedos and bombs and the weapon cabin gets a warming system to keep the weapon in standby condiction.
The Nimord R.MK1 began to serve in 1971. It is said that this is the electronic reconnaissance variation but the UK official announcement mentioned that it is just for testing the radio and radar standards. In the appearance, R.MK1 does not have the MAD stinger.
From 1975 the 35 remaining MR.MK1s were upgraded to MR.MK2 configuration, the first MR.MK2 being redelivered to the RAF in August 1979. The MR.MK2 had a completely new avionics and equipment suite, in which all major sensors and equipment items were changed. The aircraft received a new Marconi GEC central tactical system, based on a new FM1600D computer and three separete 920ATC processors for navigation systems, radar and acoustic sensors. The old ASV-21D radar is replaced by a Thorn EMI Searchwater, which now has a colour display. The radar system can distinguish the ships, the air tube and the periscope at its largest operation range. The acoustics system is based on AQS901 sonar system, compatible with BARRA, SSQ-41 and SSQ-53, TANDEM, and Ultra active and passive sonobuoys. Communications equipment is similarly upgraded, including two AS470 radio and encrypt system.
The addition of inflight-refuelling probes (initially to 16 aircraft for participation in Operation Corporate) changed the aircraft designation of MR.MK2P and necessitated the addition of tiny swept finlets on the tailplanes.
The Falklands War also resulted in the underwing hardpoints being used by front-line Nimrods for the first time, giving the ability to carry AIM-9 Sidewinders for self-defence, or anti-ship Harpoon missiles, Stingray torpedoes, bombs or depth charges.
The planned wingtip Loral ARI.18240/1 ESM pods were added later, these requiring larger rectangular finlets. All aircraft now have both refuelling probes and ESM pods.
For operation from Seeb in Oman, during Operation Desert Storm, a number of Aircraft were drawn from Nos 120 (lead), 42 and 206 Sqns to form the Nimrod MR Detachment. Several were modified to what was (unofficially) referred to as Nimrod MR.Mk 2P(GM)(Gulf Mod) through the addition of an underwing FLIR turret on the starboard wing, BOZ pods and a TRD (Towed Radar Decoy).
