Like most military weapon systems, torpedoes have also undergone repeated developmental cycles in the past. A very effective weapon at sea, certain essentially old concepts in the use of torpedoes need to be carried forward using new technologies, especially in the form of long-range delivery missiles that have torpedoes as payload. The author explains such concepts, reviews them through the experience of the Ukraine War, and feels that there is a requirement for all stakeholders to come together and blend both simple and complex technologies to develop torpedoes further.
For about two years or so, there have been sporadic media reports about the Defence Research and Development Organisation (DRDO) doing work on a variety of missile systems (or guided rockets, if you will) that could deliver a lightweight torpedo as a weapon against submarines. With the acronym “SMART”, the “Supersonic Missile Assisted Release of Torpedo” seems to be an already available missile with an anti-submarine torpedo as its payload. This article examines the issue from several angles and, in fact, suggests that this somewhat old idea needs understanding, revival and tactical-operational imagination to enhance its versatility. One hopes its development and operationalisation receive unstinted support from all stakeholders.
This piece carries forward themes of earlier articles and recorded discussions on StratNews Global and Bharatshakti.in examining lessons from the ongoing Russo-Ukraine war. Some of the takeaways are that new technologies are being married to older weapons; the large requirements for diverse types of ordnance; lessons (almost alarm bells!) for India to seriously look at ramping up ordnance development, larger ordnance stocking and new ways of delivering ordnance on target, etc. This writer hopes that this essentially “SMART” idea is not “torpedoed” in our sometimes-labyrinthine processes.
Old Wine in Old Bottles!
Sea mines used to be called torpedoes in the 19th century. These were either moored, laid on the bottom or allowed to drift into a vessel’s path and explode on contact. In the decades that followed, they became more sophisticated and could be triggered by various acoustic, magnetic, and hydro-dynamic influences. When newer forms of propulsion, both internal combustion, compressed air, and electric motors, appeared, it led to what – in hindsight – seems a fairly rapid assimilation to develop weapons that were sometimes called an “automobile torpedo.” While we need not go any further into history, including the continued relevance of sea mines, we could note a few points:
- Early versions were essentially anti-ship weapons because submarines were in their infancy and in very few numbers. They could be engaged faster with medium-calibre, quick-firing guns if caught on the surface. In both the Russo-Japanese war of 1904-05 and in WW1, mines and torpedoes were cheaper and more effective weapons of war than were “big”-gun battleships.
- The physics of underwater explosions results in pulsating “bubble” explosions that ultimately create much higher peak overpressure values than an aerial burst. For a surface ship, an explosion below, but close enough to the hull, can throw even a large ship bodily upwards and then cause it to slam back. Often this can literally break a ship’s keel, much like snapping a spine. Even otherwise, such explosions cause internal damage to equipment, causing the hull and piping to crack, thus setting off fires and flooding, often both.
- As for any other weapon, defensive counter-measures did sometimes develop after longish intervals or under urgent pressures due to combat losses. Again, just as the kill probability of offensive weapons (like torpedoes or missiles) cannot be 100 per cent (and statistically in combat conditions could be much lower), the effectiveness of defensive counter-measures against torpedoes could be relatively lower, especially when compared to anti-missile systems.
- Homing torpedoes – using a ship’s underwater noise (mainly from propellers) – appeared in WW2, first with the US Navy in their aerial torpedoes and later heavyweight torpedoes that Nazi U-boats were equipped with. Both had technical shortcomings that were eventually overcome. All modern torpedoes are homing weapons.
Old Grapes into New Wines in New Bottles
In recent decades, torpedo effectiveness has also improved across many ways in which new technologies have mattered for propulsion efficiency, leading to more silent weapons, greater endurance and range, higher lethality due to the impact of better homing, better explosives, multi-channel proximity fuzes and resistance to counter-measures. Submarine-launched heavyweight torpedoes (HWT), being of larger calibre (usually 21 in diameter), can be of much greater ranges than lightweight (LWT) versions (usually 12-14in diameter); many versions have wire guidance. However, LWTs torpedoes also have greater ranges today than slightly dated HWTs. Of course, HWTs do have much greater lethality due to a much larger warhead. Contemporary warships usually carry LWTs. Soviet/Russian and earlier-era ships of Western origin carried/carry heavy-weight ASW torpedoes but in limited numbers.
Revival of ASROC?
During and for some years after WW2, the ranges at which a ship could attack a submerged submarine were not very different from the ranges at which the U-boat could be detected. This began changing with ship-borne helicopters and ASW patrol aircraft that could look for dived submarines at greater ranges from a ship or force, mainly with dipping sonars or sonobuoys or magnetic anomaly detection. In addition to torpedoes, ships were equipped with Rocket Assisted Torpedoes (RAT).
Essentially, this was a missile fired on a ballistic trajectory with a payload of a light torpedo, which was the Mk 46 LWT for some time. It could also carry a nuclear depth charge. The torpedo would be released in a tactically suitable position near a likely enemy submarine and then home on to it. The payload descent rate would be retarded by a parachute. The ASROC, with modernised torpedoes, was especially ubiquitous in the US and some of its allied navies from about 1960-1990s when it was phased out. The reasons for this were a combination of shipborne nuclear depth charges being taken off the inventory; the somewhat limited range of the carrier missile; the reduction of the Soviet threat; and onboard magazine space pressures for other types of weapons in vertical launch systems (VLS), and so on.
However, the thinking changed again in both the US as well as the Chinese navies. The PLA Navy already has the “Yu-8” ASROC fitted on the type 054A frigates, probably within the 50 km range, until torpedo release. It now seems to be developing a longer-range ASROC of 100 km or higher. There are reports that truck-mounted versions are also likely to be in the offing. In the USN, the RUM-139C ASROC is fired from the standard Mk 41 VLS and now carries the Mk 54 Torpedo. It is good that the DRDO and the Indian Navy also seem to be keen to develop Indian ASROCs.
Furthering Utility by Exploiting Torpedo and Carrier Missile Versatility
It is difficult to make out from media reports what the contours of the indigenous development of ASROCs are. Here are some personal thoughts and suggestions about this.
Improved Domain Awareness
Due to improved multiplicity and overlapping sensors of composite ISR (Intelligence, Reconnaissance, and Surveillance) from space, cyber, aircraft, one’s own naval and shore sensors including underwater sensors etc., there is rapidly improving domain awareness that enables search, detection, localisation and fairly adequate queuing data for delivering ordnance on target on ships and to an increasing extent on submarines as well. International cooperation on MDA could further the overall ISR capabilities.
Reduced “Time Late on Datum”
A naval tactical term means that the estimated position (EP) of a submarine detected by any means (including evidence of a torpedoed ship) results in an area that keeps growing with time. The ability to rapidly deliver torpedoes by high sub-sonic or even supersonic missiles close to the target expeditiously reduces the “Time Late” consequences and a higher probability of the torpedo homing onto the target.
Need to Develop Anti-Ship ASROCs
LWTs are quite commonly thought of only as ASW weapons for air, missile, and shipborne delivery. That they first appeared as anti-ship weapons and continued to be so even for ships against surface ships during WW2 (for example, the Japanese Long Lance torpedo) is now just a memory. Against WW2 aircraft carriers, torpedoes launched by submarines and torpedo bombers accounted for many of the 38 aircraft carriers sunk in that war; (the tally was British: 8; American 11 and Japanese:19).
The modern notion that carriers, as combat ships, are very difficult to sink is a flawed one, especially if someone makes torpedoes a weapon of choice or in combination with anti-ship missiles that are being developed. WW2 statistics are interesting: 17/38 were targeted by submarines with torpedoes, another two by aerial torpedoes, and six by a combination of aeroplane bombs and torpedoes. One may add that torpedoes sank four USN battleships in the Pearl Harbour attack and several others elsewhere in the war in all theatres.
Dual Use Ordnance
Most current torpedoes fired by submarines are selectable for use against ships or submarines. Light or heavy ASW torpedoes can be modified for Anti-Surface ship (ASuW) use. This requires selectable changes in depth keeping, homing characteristics and proximity fuze triggers. It is not a technically intimidating task.
Putting ASuW Torpedoes to Use
Because of the greater efficacy of detecting surface ships more persistently and with rapidly improving positional and predictive accuracy, firing a high-speed ASROC with a torpedo as a hard-kill weapon within a few kilometres of an enemy surface or merchant ship (if so required) is now realistic. We need to develop the ASROC not only to equip surface ships but indeed from diverse locations.
Multi-Dimension Launch platforms
Such “SMART” weapons could also be launched from shore-based missile batteries along a coast or from islands or from larger aircraft, including those for maritime patrol or heavier bombers. This is precisely what is happening with anti-ship missiles (which also can be dual use against land targets) in several countries, including India.
The multiplicity of ASROC Versions
Consequently, one hopes that DRDO and the Indian Navy create a family of existing and future missiles of ranges between a100 km to even 1500-2000 km and speeds from high-subsonic cruise missiles to supersonic cruise and ballistic/hypersonic missiles. In concert with other anti-ship missiles, torpedoes in water – or the threat of torpedoes in water – could create new tactical pressures on adversaries and opportunities for multi-dimensional operations. In many cases, the same missile could possibly carry other types of ordnance as may be needed in time to come.
Of course, there will be challenges to be overcome in the various stages of technical matters as well as in tactical use. Besides, no platform or weapon system is without limitations. It does not help to read the oft-used “game-changer” exaggeration routinely observed in media for the SMART either, just as it is for almost every new platform or weapon system.
The “Atmanirbhar” and Cooperative Advantages
More so than in other naval or military operational-tactical sectors, the developmental story of Indian weapons, sensors and torpedo countermeasures is something to be quite proud of. The Indian Navy has been a key and keen participant in all this. To that could be added the growing private sector contributions in R & D spanning software, fuses, explosives, propulsion, electronics, and materials as well. We have a winning formula here. A final factor needs to be mentioned. Reports and reflections seem to suggest that in addition to matters of MDA and UDA, related security/technology cooperation bilaterally with some other nations and even “quadrilateral” should be further leveraged.
The ongoing conflict in Ukraine drives home some old fundamentals even as it demonstrates imaginative techniques of marrying old and new methods. One example is the use of sophisticated drones that are technologically advanced but relatively low-cost to release conventional grenades onto vehicles with a helpful degree of precision. The use of unmanned “Kamikaze” watercraft with sophisticated technologies that help to guide and control them until impact is but a variant of a more basic manned suicide boat that targeted the USS Cole in 2000 in Aden. Tactical imagination and improvisation are part of the processes of marrying complex and simpler technologies and hardware for greater combat effectiveness, much of it under the pressures of an ongoing conflict.
It is hoped that all stakeholders in our country continue to drive themselves hard in developing these pointers for such a family of ordnance. All this is a combination of old wine in new bottles, new wine in old bottles and new wine in new bottles. Call it what you will, we need not feel heady about this, but it could give a bad hangover to adversaries. For a ship or submarine, the alarm report of an incoming “Torpedo, Torpedo, Torpedo” usually presages some unpleasant consequences, if one is to put it mildly!
Rear Admiral Sudarshan Shrikhande, IN (Retd)