The mighty nimrod

IN THE LATTER HALF of 1942, German U-boats were sinking an average of 750,000 tons of Allied shipping a month — the Battle of the Atlantic was being lost. Not only were the vital cargoes not getting through but ships and merchant seamen were being lost faster than they could be replaced. Within a year the situation had changed and the U-boat ‘happy time’ was over as their losses rose dramatically.

This turnabout was in large part due to the increase in the anti-submarine capability of Coastal Command, air cover of the convoys in previously unguarded areas meant decreased losses of shipping — even if the aircraft didn’t achieve a kill on its U-boat, at the very least it prevented an attack on the convoy, with every chance that the U-boat would be unable to find the convoy again.

The lesson had been a long time in the learning and the experiences of World War One appeared to have been forgotten. In the interwar period a number of RAF flying-boat squadrons had an anti-submarine role, although often this simply involved patrols around the fleet to locate submarines and then direct surface vessels to the area. Development in airborne anti-submarine tactics and weapons fell behind the development of their protagonists, partly because the Admiralty considered that the shipborne Asdic system had made the submarine so vulnerable as to be redundant! The realisation that this was not so led to much improvisation and eventual success.

The lesson was not forgotten again in the postwar period, and aircraft have remained a vital link in the defence chain against submarines; although the helicopter has, of course, come into its own in the short-range point defence ASW scenario for naval task force protection. Nevertheless, the Long Range Maritime Patrol Aircraft has a vital role to play in the strategic scenario with its ability to set up search and block patterns to prevent hostile submarines moving through critical defence zones.

Since the development of the nuclear-missile armed submarine the airborne AS role has become even more vital. The ability of the submarine to sink major surface vessels was demonstrated in the Falklands War of 1982 with the loss of the Argentine Cruiser, General Belgrano. The threat to the Task Force from Argentinian submarines caused many a sleepless night — especially with the lack of land-based maritime air cover.

Aircraft

Intended as a replacement for the Shackleton, the Nimrod was developed from the successful Comet airliner. It was designed to combine the advantages of high altitude performance, and fast transit speeds, with low wing loading and good low speed manoeuvring capabilities in order to operate in its primary roles of ASW, surveillance and anti-shipping strike. The first two aircraft were conversions from Cornels, while the first production Nimrod MR. I flew in June 1968, the type entering service the following year.

It was the first (and only!) land-based four-jet maritime recce aircraft to enter service and as such was a world leader. In due course Nimrods equipped five RAF maritime squodrons, with the four UK units still operating the type today, although the ‘Options for Change’ defence cuts have recently brought a re-shuffle. Two major upgrades have taken place — to MR.2 standard in the mid 1970s and to MR.2P standard (AAR capable) in 1982 as a direct consequence of the Falklands conflict. In recent years attempts have been made to keep the aircraft ‘up-to-date’ by fitting new avionics, ESM and weapons systems, a sensible and effective policy as there is nothing wrong with the basic airframe or its capabilities.

Nimrod, ‘the Mighty Hunter’ is certain to remain operational for at least another ten years. It must also be borne in mind that ASW is but one of the many roles which the Nimrod performs; it also has a potent anti-shipping capability as well as being a link in the SAR organisation.

The Mission

«Task in, crew to ops». The arrival of another tasking signal from Northwood and crew and aircraft are allocated for a ‘Search, Locate and Destroy’ anti-submarine patrol. The previous scene of the aircrew sitting around drinking coffee, wailing for the call from ops is transformed into an organised bustle as crew planning commences.

Each member of the crew has a specific task to perform as part of the overall planning sequence — and there is not much time before the first briefing! The Mission Support System provides the crucial information to generate the MCB (Maritime Crew Brief) with the basic details of the task worked out and co-ordinated and then passed on to the crew for detailed planning. With this to hand the crew can begin to read themselves in to the mission requirements.

Co-pilot and Routine Nav work together on the route and general area details, including the latest data from the intelligence people on activity and possible threats in the operational area. From this point on the Routine Nav becomes in effect the ‘sortie secretary’, recording and analysing inputs from the other members of the crew; this task becomes even more important in the air when the details he has recorded can be used, at any time, to ‘revise’ the mission progress.

The TacNav (Tactical Navigator) concentrates on the operational area, planning the mission tactics — based on the intelligence so far received but in the full knowledge that his basic plan will almost certainly have to change as the mission progresses.

Although the First Pilot oversees the entire mission plan, it is to the area of tactics, with the TacNav, that he devotes most of his attention; in the operational area these two will work very closely together, co-ordinating the inputs of the entire crew. The seven Sensor Operators carry out various tasks; from mission planning by the Lead Dry, looking at the EW aspects, and Lead Wet, the all-important acoustic conditions in the target area, to arranging Safety Equipment and organising rations for the sortie. The final member of the crew, the Engineer, has, meanwhile been checking on the aircraft details and, in liaison with the TacNav’s requirements, making sure that the right quantity of the right sonobuoys are loaded. Thirty minutes to briefing and the mission details are nearing completion — operational area plotted, combined search pattern tactics outlined, route details complete, intelligence data analysed and plotted, aircraft load confirmed. A final check around the crew for any other inputs a last-minute change in intelligence puts a Soviet (CIS) Krivak guided missile frigate in the area, its SAN-4 missiles are a formidable short/medium range defensive system and it is a vessel to keep well clear of if at all possible. This general briefing by the MSS stafr takes about 15 minutes, data is stored on computer and flashed up onto the screens in the briefing room — the overall intelligence plot reveals the complexity of the situation and highlights the need for ESM monitoring during the transit to the task area.

Load all the kit onto the crew bus and out to the aircraft, one hour twenty minutes to takeoff the hydraulics snag which the Engineer discovered on his earlier inspection of the aircraft has been rectified and the Nimrod looks all set to go — if all the systems check out. Each member of the crew must carefully check his area of responsibility and systems — nav kit ON, set and checked, computer programmed with the mission tape and route checked . . . TacNav’s planned mission load of sonobuoys checked by the ‘Wet’ men and programmed into the computer. The Nav confirms that the weapons load is as programmed; the six Stingray torpedoes in the bomb bay give the Nimrod a mighty punch.

A more accurate description would be underwater guided missile as Stingray works more like an AAM than the traditional idea of a torpedo. An acoustic homing system in the nose activates as the ‘missile’ enters the water and from then on the on-board computers take over and control the attack. The torpedo becomes a sub hunter with the sensors and computers working out the ideal attack for the type of target detected; the net result is the best impact parameters for the highly effective shaped-charge warhead.

Radios, radar, EW equipment — all are checked, all form part of the Nimrod as a fighting system. The back of the aircraft is a hive or activity as each crew member runs through his preflights, cross-checking with other crew stations as required. The integration of all the individual elements is the key to the effectiveness of the system in its task of finding and killing submarines.

A snag on the VDUs of the nav station needs the attention of a ground technician — how much delay will this cause, can it be fixed, if not can the mission go ahead without this item …. a multitude of thoughts as the minutes tick away towards the brakes off time . . . Try again to recycle the VDUs by switching on and off and resetting the circuit breakers.. . no joy, one more go … the screens blink and then stabilise; as so often happens with electronic equipment there doesn’t appear to be anything wrong — if at first it does not work, try it again!

At the front end it is the same for the pilots with the aircraft and flight systems getting the once over. Thirty minutes to take-off, time to start the engines, crew check in with status of systems ready for the engine start… so far the systems look good. Crew chief confirms clear for No 3 engine… light up, indications good and the gentle rumble through the airframe sounds and feels about right. The other three Rolls-Royce Spey 250s lignt up in turn and stabilise at idling as the Engineer surveys his panels for the least sign of any problems; these panels are in effect the ‘health monitoring’ of the aircraft’s engines and associated systems — the experienced Engineer will detect the slightest flicker of a needle, the merest hint of a flaw developing, long before the aircraft alarm systems will show it up.

At the end of the runway with engines at full throttle the aircraft judders under the strain, held by the brakes… final checks, cleared to go . . . brakes off and accelerate down the tarmac. Speed builds rapidly «VR» back on the stick and the Nimrod rises into the air. Minutes later the aircraft is out over the sea and on its own. Although the task area is some way away there is no shortage of tasks to be performed, all with the aim of getting this potent weapon system to its designated area in one piece, on time and ready for action.

«Tattiul Checks Outbound»

The list is quickly completed to bring the aircraft systems on line with weapons checked, serviceable, but not as yet armed. Much of the routine interchange of information between the Tac-crew is made off the aircraft’s intercom, a piece of data is passed from one computer screen to another, a shouted instruction or series of numbers — to clutter up the ‘airwaves’ within the aircraft would be counterproductive, so much has to be relayed that there would hardly be a second of quiet! Keep the intercom for essentials. ESM reports picking up a Soviet early warning radar . . . classified as probably a Headnel … no other supporting electronic data but a radar sweep confirms a surface contact in the area, assessed as likely to be a warship. Headnel is carried by numerous Soviet vessels, some would pose an immediate threat, others not, but no point in taking the aircraft that way, an alteration of course keeps well away from any trouble.

Listen and look . . . monitor of the systems from radar to EW helps build up the picture of what is really happening in the area rather than the ‘perhaps’ scenario provided at the planning stage. Does it change the overall tactical plan? What is the significance of that piece of EW information? ESM reports airborne pick up, classified as a Bear-D, recorded bv Routine Nav, relayed to Maritime HQ . . . The picture is continually changing and the TacNav’s screen takes on the role of tactical map of his area of interest. Approaching the task area and time to go down to low level.

«Tactical Checks on Task»

This brings the aircraft into a state where it is ready for action — weapons checked and armed and sonobuoy launchers loaded . . . final tactical briefing by TacNav for radar search and carefully structured pattern (field) of sonobuoys. Level off, radar check to assess picture — ON, quick check on clarity and discrimination of picture, OFF. The idea is to try and achieve surprise, catch the submarine unawares so that it cannot dive into the sanctuary of the depths. The general surface plot of the area, if any, has already been established on the screen by the radar search from outside of the area and the combined search pattern can be established. As the aircraft flies its pre-planned radar search the pattern of sonobuoys is dropped until the ‘field’ is complete.

With the search pattern established the routine of looking and listening becomes even more intense. Those members of the crew not actively engaged with monitoring systems scan the waters and sky from the bulging domes of the port and starboard beam positions for contacts and threats, low level over the sea is no place to get bounced by an aircraft! (Even though Nimrods have been seen sporting a pair of Sidewinder missiles for self defence).

Acoustic reports contact from a sonobuoy suggesting that a diesel submarine is in the area re-charging its batteries, the diesel engine noise being picked up by the sonobuoy.

«CAPTAIN, ACOUSTICS .. . CONTACT IN LOFAR ZERO NINE… ANALYSING.» Almost instantaneously the situation is assessed and the aircraft turned towards the relevant sonobuoy. The contact must be within an area centred on the sonobuoy and it is from there that any attack should commence. «POSSIBLE SUB. DIESEL SUB.»

Rolled out heading towards the area, acoustics listening out for sonobuoy data and relaying to the TacNav. The battle plan formulates … get to the target before it detects the aircraft and tries to escape, set up for a good first pass attack — while preparing a pattern tor any target-orea search should die submarine vanish at the last minute. Relay data to the radar ops screen for the radar search area and pattern required when called for, plus a quick verbal brief on how the TacNav wants to play it. , . call for radar on at appropriate range to scan the contact area …

“CAPTAIN, RADAR . . . HIGH CONFIDENCE SNORT TWO SEVEN ZERO DEGREES FIFTEEN MILES, RADAR FILE TWO-FOUR.»

With this data fed into the CTS (Computer Tracking System) the nav initiates a steer towards the target.

Twelve miles to contact area, all systems look good, still held on acoustics and radar; the weapons are primed and ready, aircraft running in at max speed to reduce the sub’s evasion time … the pilots begin to scan the area ahead of the aircraft — surely the sub must dive before the aircraft reaches it, very few people are lucky enough to get in a full visual attack.

«ON TOP… NOW, NOW, NOW.» Overhead the in-contact sonobuoy and the attack continues.

«CAPTAIN, RADAR. CONTACT LOST. SINKER. ELEVEN MILES. DATA FILE TWO-FIVE.»

It is no great surprise that the aircraft has been detected and the sub has gone into an evasive dive. The tactical plan has allowed for this.

Continue towards the datum to set up an attack pattern.

«TEN MILES. NO CONTACT WITHIN FIVE MILES OF DATUM.»

«ACTION STATIONS. ACTION STATIONS. PREPARE FOR MAD.»

Acknowledgement of the MAD instruction confirms that yet another of the detection systems is ready to go. The Magnetic Anomaly Detector will detect any changes in the water caused by the passage of a large metallic object — like a submarine! TacNav briefs his final intentions for the attack.

«FOUR MILES. BOMB DOORS. HRD.»

The underneath of the aircraft parts to reveal the weapons bay and its cargo of torpedoes. «ONE AND A HALF MILES. SEARCHLIGHT.»

As the co-pilot switches on the searchlight the nav calls that the aircraft has entered the likely MAD area and the pilot confirms that the aircraft is configured for MAD. Still no contact re-established and although the nav is ready to drop the weapon on a MAD mark it seems inevitable that a new pattern of sonobuoys will have to be laid. Overhead the datum lay a pattern of active sonobuoys in a circle around the ‘target’ position.

With the field set the nav puts the aircraft into a MAD-trap circle around the area, waiting for any tell-tale indications, and ready to let loose the torpedo.

And so the waiting game, cat and mouse, begins. The submarine will be looking for a way out of the trap — a change of speed, direction or depth — the aircraft with its array of sensors looking and listening, predicting what its prey will try and do next. Some buoys are keyed to look for the sub that tries to run for it, others concentrate on the ‘hider’ who sits still and pretends not to be there. «CAPTAIN, ACOUSTICS. FIX ACTIVE TWO FOUR. ONE EIGHT ZERO SIX MILES. FILE TWO NINE.»

The call from the acoustics monitor tells the TacNav where the contact is reference to a particular sonobuoy and this is quickly assessed on the tactical display.

The display in front of the TacNav automatically takes on the new data and shows the plot of the target position as a row of diamonds on the screen. In theory, at any given time, the submarine is at the position of the last diamond to be displayed. Select target tracker to bring the computer predictions into the loop … a few more acoustic plots and the computer gradually pins the position of the target down …

With the call from the TacNav the Nimrod swings around towards the in-contact sonobuoy as the attack is set up.

Prediction looks good, attack track established, weapons selected and parameters set.

Again the sonobuoy loses contact, the submarine has manoeuvred out of its area . . . does the computer prediction cover the change, what is the submarine doing, no time to reestablish a sensor contact — continue on this attack or adjust the profile by trying to second guess the opposition …

«HARD RIGHT… WINGS LEVEL.»

Having made the decision to take a manual correction there is only time now for the nav to select the computer ballistics and finalise the attack. Countdown from 10 to zero … hit the weapon release button and check that the orange light on the store select panel goes out. At almost the same instant the MAD mark corroborates the computers calculations. The confirming call of «Weapon Away» from the crewman monitoring the bomb bay periscope as the Stingray torpedo clears the aircraft, its parachute deploys and it slices into the water. Water entry is picked up by the acoustic monitors, who also confirm from the distinctive ‘pinging’ that the weapon is under way…

«TORPEDO RUNNING.»

The aircraft is cranked into a holding pattern over the entry area . .. ready to make further attacks . . the seemingly interminable wait whilst the torpedo runs its course, a matter of minutes at most, but feeling like much more.

«LOUD UNDERWATER EXPLOSION.»

Confirmation that the lethal Stingray has found its target, a hit is a kill, as the chances of a diesel submarine surviving a Stingray impact are minimal. One down, but how many more might be lurking in the task area — no time to sit around. Whilst running through the post-incident check list, getting the aircraft systems set back to search mode, refilling the sonobuoy launchers and selecting the next weapon, the Nimrod climbs back to patrol height and re-establishes the search pattern.

There could be many more hours of looking and listening, and perhaps even another attack to carry out, before the patrol comes to an end and the aircraft is recovered to base. The duration is limited more by the number of sonobuoys and weapons carried rather than by any other factor as the Nimrod is AAR capable and can call for a tanker if required. Airborne four hours and time to replenish some of the energy expended on the first attack as the on-board galley comes into its own as a source of hot food!

Gull War Participation

One of the most important aspects of the original United Nations sanctions against Iraq was the isolating of that country by air and sea. Strong naval forces were deployed to the Gulf with instructions to challenge, including stop and search missions, all shipping bound for Iraq. Maritime air power, and especially the RAF Nimrods, played a leading role in ‘ this task by monitoring all shipping and, when required, directing surface forces to make an intercept.

This work has been virtually ignored in all accounts of Desert Shield and Deserf Storm.

With the commencement of hostilities the Nimrods were involved with active anti shipping operations, again in conjunction with surface forces. They also flew a number of special tasks, the nature of which is still something of a mystery.

Acting as an airborne control and coordination system (a la AWACs) using its Searchwater radar plus extensive communications suite (enhanced for the Gulf War), the Nimrod proved remarkably successful; the Nimrod/Lynx/Sea Skua proved to be an effective team.

Future Developments

The Nimrod has proved itself an outstanding aircraft for its designated roles and as long as the aircraft’s systems continue to be upgraded, to meet the changing requirements of its roles, then there is no reason why the aircraft should not keep going for many years (despite recent fears of corrosion problems).

The next major update on the aircraft’s systems is due to take place in the early 1990s although details of what this will involve are not yet known. Aircraft replacement has been postulated and if such did materialise it would almost certainly involve purchase of one of the American Long Range Maritime Patrol aircraft now under consideration or development.

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