A Sample Feature From Aviation News

NIMROD The Versatile Hunter

In the first of two articles on the Nimrod maritime patrol aircraft, Dino Carrara reports on how the aircraft has had to adapt since the end of the Cold War.

A line-up of Nimrod MR.2s at RAF Kinloss. (Photo, Aviation News).

THE Nimrod MR.2 is best known for its anti-submarine warfare (ASW) role; however, recent conflicts have required it to focus on surface vessels in the anti-surface unit warfare (ASUW) mission. These two, plus other tasks it can perform emphasises just how capable this aircraft and its systems are. This is set to be further improved when the Nimrod MRA.4 enters service.

The Nimrod fleet and its crews have, like the rest of the armed forces, had to adapt to the changing threats since the end of the Cold War. When the Soviet Union still existed with its massive submarine fleet, the aircraft would spend the majority of their time in the open ocean far from land trying to locate and keep track of these submarines. This task is still important as despite the reduction in numbers, Russia still possesses some very capable and active submarines.

Nimrod MR.2s overfly their home base of RAF Kinloss. (Photo, Crown Copyright/RAF).

A typical Cold War scenario, and still undertaken today to a lesser extent, would see the aircraft dispatched to a sector of the ocean where intelligence sources had determined a submarine to be operating. The aircraft would descend to low-level and drop a line of passive sonobuoys (called ‘the barrier’) through which it was expected their target would transit. There are three types of sonobuoy, passive which listen, active which emits signals and what is called a bathy buoy which gives a temperature profile with depth. This is required to determine how sound will travel through water and hence determine ranges. Each sonobuoy is set for a particular depth, the body floating on the surface while the hydrophone descends to the pre-set level. On occasions submarines have surfaced to try to capture these advanced listening devices, as a result they can be commanded from the aircraft to sink and thus prevent capture.

A crew member prepares a sonobuoy, prior to it being dropped from the aircraft. On the left are the racks where these listening devices are kept. (Photo, Aviation News).

The passive sonobuoys are designed to listen and not emit signals, with the aim of preventing a submarine from realising it is being tracked. The data gleaned from these aquatic ‘ears’ is transmitted to the Marconi AQS 901 Acoustics Processing and Display System for analysis. Designed in the 1970s, this is currently being replaced by the AQS 971, developed by Computing Devices Canada (CDC) and Ultra Electronics, which is a great improvement. The magnetic anomaly detector (MAD) boom at the back of the aircraft is also part of the ASW equipment which can recognise disturbances in the earth’s magnetic field by the presence of a metallic object under the water, such as a submarine. The Racal Searchwater radar can also be used, as it is capable of detecting a submarine on the surface, a snokel (more widely known as snorkel) from a diesel submarine as it takes in air or even a periscope.

If a submarine is detected and designated as hostile in wartime it would be attacked with Stingray torpedoes which are carried in the bomb bay. The aircraft’s crew would attempt to remain undetected until their torpedo entered the water, hopefully giving the submarine a nasty surprise.

New challenges

The number of countries adding attack submarines to their fleets, such as India and Iran, has grown in recent years as they realise the benefits and threat these vessels can pose. This has meant that the task of ASW often now has to be practiced in different environments than was the norm in the Cold War. The new challenge faced by Nimrod crews is to locate submarines that operate in the littoral (close to shore) or shallow waters. This provides a number of extra factors that have to be considered compared with an open, deep ocean environment. For example, an enemy’s submarine may stay relatively close to shore to seek the protection of its air force and surface-to-air (SAM) batteries from aerial attackers, such as Nimrod. For these reasons it is more demanding on the flightdeck crew as they have to be more spacially aware. Also, the underwater conditions are noisier closer to shore due to passing ships in often busy coastal waters, sounds from the land, plus the fact that there is more marine life than in the open ocean, all make it harder to hear a submarine. Equally, the electronic environment is far more congested than would be the case in the latter.The acoustics team on the aircraft also have to contend with shallower depths where the sensors perform differently to deep water.

The cockpit of Nimrod MR.2, XV255, with its banks of dials. These are to be replaced with multi-function displays in the MRA.4. (Photo, Aviation News).

The submarine does not have it all its own way as in the shallows there is less room to manoeuvre and thus fewer places to hide. A good example of this type of environment is the Arabian Gulf which is both narrow and shallow. Due to the challenges this type of environment can pose extensive training takes place to hone the skills of the crews and as a result many exercises are conducted in these or similar locations. A recent example was Exercise JMC 012 in June this year, which saw a lot of activity in the confines of the Minches, the area of sea between the Outer Hebrides islands and the Scottish mainland.

Anti-surface unit warfare

As mentioned initially, recent conflicts have required the aircraft to utilise its Anti-Surface Unit Warfare (ASUW) capabilities. The amount of training given to this role is now roughly the same as for ASW. This task entails the aircraft forming a picture, using its Searchwater radar, of all the surface contacts to monitor shipping movements. This information can be used for a number of purposes such as maritime reconnaissance or watching for sanction busting ships such as in the Arabian Gulf, for example. The same data can be used for it to launch an attack using Harpoon anti-shipping missiles, two of which can be carried. It can also provide targeting information to other aircraft tasked in the anti-shipping role, which used to include the Tornado GR.1B with Sea Eagle missiles. However, this weapon has been withdrawn from the inventory and as a result the role has been relinquished by the Tornado force. The only other UK airborne anti-shipping platforms, other than the Nimrod MR.2, are the Royal Navy’s Lynx using the Sea Skua missile. This targeting role was practiced during JMC 012 with Nimrods directing strikes by US Navy F/A-18C Hornets from the USS Enterprise supported by F-14A Tomcats providing protection with assistance from S-3B Vikings also scanning the surface picture and the airspace being monitored and controlled by E-2C Hawkeyes. The Nimrod community also works with other Nato anti-shipping aircraft such German Marineflieger Tornados and Aéronavale Super Etendards.

. . . For the full article see the December issue.