Torped 47 – Steel fishes back into Finnish service

On the evening of 18 November 1942, three Finnish motor torpedo boats entered the Soviet port at Moschny Island (Fi. Lavansaari) and fired four torpedoes which sank the Soviet 1,700 ton gun boat Krasnoye Znamya at its moorings, after which they sped away unscathed. The daring raid is the high point in the history of Finnish torpedoes, and five years later torpedoes were effectively banned from Finnish use with the Paris Peace Treaty.

Like the case with guided missiles, the ban would in the end give way to Soviet weapon exports. In this case torpedoes reappeared on the (official) Finnish TOE with the acquisition of two Project 50 ‘Gornostay’ (NATO-designation ‘Riga’-class) frigates in the mid-1960’s, both of which sported heavy torpedoes (533 mm). The local renaissance of the torpedo was however cut short by the fact that the ships themselves weren’t overly successful, and importantly they were too manpower intensive for the small Finnish Navy. In the end, they were retired in 1979 and 1985 respectively.

Now, while the heavy torpedo slowly gave way to the anti-ship missile as the premier weapon in ship-to-ship combat, the lightweight torpedo became the anti-submarine weapon of choice for most navies in the world. In Finland things were a bit different, mainly because of the shallow and constrained waters which dominate the northern shore of the Gulf of Finland. However, things slowly started to change with the introduction of ever more capable diesel-electric submarines and different kinds of midget submarines in the Russian Baltic Fleet. While running towards the enemy at speed and throwing depth charges might have worked against a Project 641 ‘Foxtrot’-class, it was very doubtful whether it would against more modern designs such as the current Project 877/636 ‘Kilo’ or the upcoming Project 677 ‘Lada’.

With these developments under the surface in combination with the Finnish Navy shifting more and more priority from defence against enemy amphibious landings/naval movements to protection of merchant shipping, it was clear that the ASW-capability needed a boost. There simply needed to be more ships capable of performing ASW, and they needed a longer reach to avoid being sunk outside of the range of their own ASW-weapons. Enter the second reintroduction of torpedoes into Finnish service, with the decision that the Hamina-class and the upcoming Pohjanmaa-class (Squadron 2020) would both get light torpedoes.

The choice of torpedoes was revealed early January this year, with the announcement that Saab’s new lightweight torpedo (NLWT) had been chosen. As a matter of fact, the torpedo is so new that it hasn’t got a company name yet. “There is a name in the works”, Saab’s sales director for underwater systems Håkan Ekström discloses. In the meantime, the Swedish Defence Forces has already named the new weapon Torped 47 (sans-o, as that’s how the word is written in Swedish).

That Finland would opt for the NLWT was rather unsurprising, considering that it is highly optimised for the kind of littoral environment that any Finnish submarine hunt would take place in. Compared to ‘blue waters’ (open seas), looking for submarines is vastly different in the Baltic Sea. Detection ranges, and combat ranges for that matter, can easily be much greater than the depth, leaving the combat taking place in what the product manager for torpedoes, Thomas Petersson, described as a “Thin slice of water”. This causes issues for active sonars, as in the oceans anything spotted by them is usually either a submarine or some kind of sealife. In the Baltic Sea, most echoes are simply coming from the seabed, leading to a more difficult discrimination problem. The water also has some interesting behaviors, part of which comes from the many rivers flowing into the sea. These bring fresh water of various temperatures and significant amounts of sediments into the sea, leading to sound waves in some cases experiencing refraction in two directions (see this short and nice primer on how different temperatures messes up submarine hunting). In short together with the cluttered seabed detection becomes difficult, leading to relatively short engagement ranges.

Saab’s answer is the NLWT, which sports a number of niche features which combine to address the problems of subhunting in littoral waters. To begin with the torpedo is wire-guided, meaning that the operator aboard the ship can easily control the torpedo throughout its course. This also allows it to be used like a forward-deployed sensor, in that the operator can use its active sonar to look for targets, at different depths, as the torpedo is happily moving towards the suspected submarine location. The torpedo also has a very low slowest possible speed, allowing it to run very silently, further increasing the effectiveness of its sonars (the torpedo can be fired in both active and passive modes). One crucial difference is that the active sonar is operating at a somewhat higher frequency than usual for light torpedoes, giving it better resolution on the sonar picture as a tradeoff for somewhat shorter viewing range. The torpedo also has a quick launch sequence and rapidly goes into stable running, to ensure that it doesn’t touch the bottom and can handle the earlier mentioned short engagement ranges efficiently.

For the technical specifications, NLWT is made out of aluminium, and sports a pump jet with a single rotating impeller and a stator in place of the earlier Torped 45’s two unshrouded coaxial counter-rotating screws. The battery has also been upgraded, with lithium iron phosphate (LiFePO4) batteries replacing the earlier silver-oxide. This allows the torpedo to stay launch-ready for longer times in the launch tube, which also functions as the plug-and-play storage tube. The launch tube also include pressurised air to eject the torpedo and a spool of the same wire as is found inside the torpedo. If the torpedo moves, the torpedo spools out wire, and if the vessel moves the launch tube spools out wire. This ensures that the wire stays stationary in the water after the first few meters of the torpedo run, making sure that it doesn’t tangle or break. In the case of a wire break the torpedo will either abort or continue in fire-and-forget mode, depending on the mode chosen before launch. After a torpedo has been launched, the whole empty launch tube is switched out to a new tube with a launch ready torpedo inside it. This switch takes around 15-30 minutes for a trained crew and doesn’t require any specific equipment other than a suitable crane to handle the load. As such, it could conceivably be handled at sea (sea state allowing). The used launch tube is then sent back to a naval base to be reloaded. The direct drive DC-motor together with the new batteries provide a range measured in “tens of kilometers”, the exact number being both classified and highly dependent upon the speed of the torpedo.

The active sensor provides a detailed enough picture that it can measure the length of the target, and any major features such as the conning tower can be made out. During the run the torpedo maps all return echoes, run validity checks, and reports on valid targets. If allowed it will then intercept the closest valid target inside the search box, and in case of a miss it will re-acquire for another attack. The seeker has been used successfully during live-fire exercises against targets the size of midget submarines, and Saab is confident that it can handle these kinds of targets as well as regular submarines. An interesting feature is the anti-ship capability, and though the small warhead (Saab declines to give the size, but notes that most light torpedoes carry a warhead weighing “about 50 kilograms”) won’t sink any major surface units, it does punch above its weight in that it has a dedicated ASuW-attack mode going beneath the vessel and using an upwards-looking proximity fuse to detonate under the keel. The combined effect of the gas-bubble which removes the water that carries that part of the vessel combined with the impact of water rushing back to fill the hole is enough to literally break ships in two when employed by larger torpedoes, and while the NLWT won’t repeat that, it will most likely send any corvette limping back to base with the hull distorted and propulsion shafts out of alignment.

Part of this performance comes from the Swedish requirement to be able to use the torpedo from both surface ships, submarines, coastal launchers, and aircrafts/helicopters. For the submarines, the light torpedo plays an important role as a self-defence weapon, as well as for hunting other submarines. For the Hamina-class, they will sport a single fixed twin launcher on the rear deck, allowing enough space for the RIB-launch to remain in its current position. Looking at the future, the contract with Saab also include an option for the four Pohjanmaa-class corvettes, and everything points towards this option being exercised within the next year or so when the acquisition of weapons for the corvette program starts to take place.

The current Finnish contract for the torpedoes include the systems for the Hamina-class and an undisclosed number of torpedoes, as well as training at the torpedo research and development center in Motala. This is also where we are shown the first prototype of the weapon, which is just about to finish its part of the development program. The production of the units themselves, and prototype number two which is currently in production, takes place in Linköping. Deliveries to both Finland and Sweden will start in 2023, and FNS Tornio, the first of the Hamina-class to undergo MLU, will be ready to go to sea with the launchers fitted already next year. Notable is that the Swedish Defence Materiel Administration, FMV, is closely involved in the project and is the launch customer that has contracted Saab to develop a new torpedo. However, the Finnish contract with Saab does not include any research and developments, but is purely for production and supply (including torpedoes, hardware needed for their operation, documentation, and training). However, at the same time the Finnish Defence Forces Logistics Command, PVLOGL, has signed an agreement with the FMV regarding cooperation and loans of Torped 45 to cover the period 2019 to 2023 when the Finnish Navy will have torpedo capable ships but no torpedoes.

‘Borrowing’ something that is literally worth millions of Euros sounded a bit suspicious to me, so I decided to contact FMV to confirm that it wasn’t just a case of Saab spelling ‘leasing’ wrong. However, FMV confirmed that it is indeed the case that the Finnish Defence Forces gets to borrow a non-disclosed number of torpedoes for free, as long as they are used and maintained according to official documentation. The aim of this agreement is that Finland will be able to operate with the Torped 45 aboard FNS Tornio already next autumn. Part of why this generosity is bestowed upon the Finnish Navy is no doubt that torpedoes occupy a rather unique role amongst modern munitions in that after launch they can be retrieved (the training warhead sports a flotation device in the form a inflatable ‘balloon’), and after the wire has been respooled and the battery recharged they are good to go again. As such, this is quite different compared to e.g. borrowing artillery rounds.

However, another angle is without doubt the value for Sweden of having Finland as an operator of the same system. Not only will this offer benefits when jointly performing ASW missions as part of the Swedish-Finnish Naval Task Group (the SFNTG), but a second cooperation deal signed at the same time between FMV and PVLOGL concern the future of the NLWT. Under this the two nations will cooperate around the acquisition and continued development of the torpedo system. By creating these kinds of synergies the costs for operating and keeping the system up to date will hopefully be lower for both users, and the agreement also open up the doors for increased cooperation around the ASW-mission as a whole.

The first draft of the text and pictures, with the exception of those parts based on information given by FMV, has been provided to Saab for screening to ensure that no classified, export controlled, or company confidential information is included.