Keeping submarines up to scratch.

Since the end of the Cold War, the rate of expansion of submarine forces worldwide has slowed and new procurements are no longer being ordered at the previous rate. Consequently, many navies are carrying out extensive modernisation of their submarine fleets, pending acquisition of new boats.

Modernisation and upgrading can extend the life of existing boats to almost 30 years, making them highly effective units in a modern naval scenario. The move towards littoral warfare has swayed the balance of submarine forces towards the non-nuclear SSK-type. However, it must be said that those navies with nuclear-powered boats, whether nuclear-missile armed (SSBNs) or attack (SSNs), still consider modernisation an important adjunct as new designs are developed. The US Navy's SSBN-to-SSGN conversion of four Ohio class boats to re-role them as guided missile and special operations forces support submarines is one classic example.

The SSGN highlights an increasingly important role for submarines: that of clandestine operations. A number of British and American boats are being fitted with dry deck shelters for the carriage of new and advanced Swimmer Delivery Vehicles (SDV). In this role, the submarine will be used to support expeditionary warfare operations. This facility could be expanded further with the possible inclusion of Unmanned Underwater Vehicles (UUV) and drones in the submarine's armoury.

Perhaps the most important aspect of modernisation must be weapon control, sensor and command functions. To remain effective, submarines today must be equipped with a fully integrated combat suite comprising sensors, combat management and fire-control system. Venezuela's two Type 209 SSKs were given a half-life refit consisting of a new fire control system, sonar, attack periscopes and new engines--the hulls being lengthened in the process to accommodate the new equipment.

As always, budgets will dictate which areas may be left untouched, although priority would probably be given to updating the combat and sonar systems. Typical of such a move is the planned modernisation of two of Italy's Improved Sauro class boats--Primo Longobardo and Gianfranco Gassana Priaroggia--with the Atlas Elektronik Isus 90 integrated combat system and a new sonar.

Wherever possible, prudence also dictates upgrading the optical and electronic warfare capabilities of a submarine. Advances in technology over the last decade have ensured improved capability in today's systems. New periscopes with infrared imaging are included in the current upgrade of Spanish Agosta class boats, together with a new ESM (Electronic Support Measures) suite, an improved fire control system and a new towed-array sonar.

With the advance into the littoral environment, the classic quality of a submarine--its silence--has assumed renewed importance, being reinvented by adoption of the aviation buzzword stealth. Thus, considerable attention needs to be paid to noise reduction techniques, especially considering improvements in low-frequency active towed array sonars. Thus exterior noise reducing cladding and interior noise reduction materials are being considered for retrofit.

With regard to propulsion, the SSK's diesel-electric powerplant, sensibly maintained, is probably worth retaining. The diesel motors themselves are hard wearing with a long life expectancy. The electric motors could likewise be retained. However, recent years have seen battery design advance considerably. When upgrading an older SSK, consideration is now given to replacing old batteries with new designs capable of charging at a high rate in a short time. In parallel, extending the battery compartment and increasing the number of storage cells would give the boat a greater submerged endurance.

Then, of course, there is the increasing consideration for the adoption of the closed-cycle air-independent engine not only for new-build boats but also in modernisation plans. German and Swedish developments in such propulsion methods are today operational. Newbuilds apart (e.g. France, Greece and Japan), Denmark has acquired the former Swedish Nacken with a Stirling air-independent propulsion system and the first two of Pakistan's three new Agosta 90B-class boats procured from France will be retrofitted with the Mesma system later (the third boat is being equipped with the Mesma on construction.)

As a long-term option Canada is also considering equipping its four former Royal Navy Upholder class SSKs with a fuel-cell system, which is currently under development by Ballard Power Systems. Insertion of an air-independent module is also possible for the mid-life modernisation of the four Dutch Walrus class SSKs, which is planned to begin in 2009.

The final area to consider is, of course, weaponry. As recent events in the Arabian Gulf and Adriatic regions have illustrated, the submarine is well suited to the task of theatre missions, deploying long-range land attack missiles such as the Tomahawk--usually from SSN-type boats--as well as providing sub-surface support. Made possible by the ability to download target data from a satellite, over-the-horizon engagements (out of range of hostile surface forces) have become SOP (standard operating procedure) for some navies. Even China is now reported to be developing an encapsulated, long-range land attack cruise missile for launch from a torpedo tube.

The emphasis on the littoral arena has meant that some navies, operating 'out of area' for the first time, are routinely carrying out missions in shallow waters that do not offer the option of 'going deep' to evade hostile forces. Consideration is now being given to improving a submarine's ability to stand and fight. The ASW helicopter is considered one of the major threats to submarines operating in littoral scenarios and a number of developments are underway to counter this threat.

Since a half-century has passed that deck guns were mounted on submarines, much attention has been focussed on detecting the threat. Today's EW systems are capable of operating in a dense electromagnetic environment alongside other systems such as satellite communications and friendly radar.

However, another solution to the air threat is the surface-to-air missile. Both the United Kingdom and United States addressed the problem of mounting lightweight air defence missiles on submarines during the 1970s and 1980s. Britain experimented with the Slam (Submarine-Launched Air Missile)--six Shorts Blowpipe missiles mounted in a container attached to the boat's sail--while the American solution was the Subads (SUBmarine Air-Defense System) version of the Siam (Self-Initiated Anti-aircraft Missile). Both efforts came to nought.

Now, the US Navy is considering adopting the Raytheon AIM-9X Sidewinder air-to-air missile for the surface-to-air role to equip its SSNs with an anti-helicopter capability. The Aim-9X would be encapsulated and launched from the vertical tubes currently used to launch Tomahawk missiles.

This adoption of an air weapon to submarine use is made possible by the missile's all-aspect seeker head which combines a 128 x 128-element staring focal plane array (cooled by an integral Stirling closed-cycle cryogenic system) mounted on a roll/nod gimbal. The seeker has a very rapid slew rate and a high off-boresight capability. ASW helicopters beware!

The above is not an exhaustive coverage of the subject but highlights areas of concern and various solutions to the problems of keeping submarine capability and flexibility in tune with emerging naval warfare scenarios.