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.

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Saab’s render of the NLWT in full ‘warpaint’. Picture courtesy of Saab

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.

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Håkan Ekström, Saab’s sales director for underwater systems. Source: Own picture

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.

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The earlier Torped 45 being fired of a ship during an ASW exercise. Note the two unshrouded screws, the most obvious external difference compared to the NLWT. Source: Jimmie Adamsson/Försvarsmakten

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.

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The first prototype of the NLWT during tests at Motala. Note orange dummy warhead, wire being retrieved in the bucket aft of the torpedo, and the grey disc on top of the torpedo immediately behind the warhead which marks the location of the proximity fuse. Picture courtesy of Saab

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.

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RBS15 – on the road to the Next Generation

“Psychedelic” is the word I hear someone standing next to me use to describe the room. I agree. We are standing inside what is roughly a 13 m long cube, with all the surfaces being covered with soft blue spikes of different sizes. The room is completely void of echoes, and they say that if you stand here alone, you will eventually hear your heart beating. Loudly. The only objects standing out is a large frame mounted halfway up one wall, and a pattern of blank discs mounted opposite the frame, these being the flight motion simulator and the antenna wall respectively.  We are in the anechoic chamber at ELSI, and I almost expect GLaDOS to start talking to us.

ELSI, or the Electrical Warfare Simulator, is at the hearth of Saab’s anti-ship missile program. The seeker-head of the RBS15 missile is mounted on the flight motion simulator, which moves the seeker in 3-axises as it ‘flies’. On the other end of the room the antennas sends out signals corresponding to what the seeker would see at any given moment during its course. This includes not only target signatures, environmental effects, and countermeasures in the form of false targets and active jammers. All this, coupled with the seekers simulated position and real-world direction, are then used to create the model, which is fed to the antenna wall’s signal generator which creates artificial radar returns for the seeker head. As noted, it is very much a case of the actual hardware being in the loop during testing.

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RBS15, sporting a 200 kilogram warhead to dissuade enemy ships from getting within 200 kilometers of your waters. Source: Own picture

The story of ELSI goes back to the early 90’s, when the board decided upon the investment, partly to ensure that Saab would be able to expand their share of the export market in an age of shrinking defence budgets. 1994 the site was running its first tests, and four years later it was operating at the desired level, a host of teething problems having been fixed.

Finland is no stranger to the RBS15, having operated the first generation of the missile from ship and shorebased batteries under the local designation MTO-85 since the late eighties. As such, a Finnish delegation visited ELSI early on in 1999, with the latest Finnish threat pictures. The purpose was to run a comprehensive round of tests with the MTO-85 seeker, which then provided the basis for an upgrade program launched at Saab. The upgraded seeker was then run through the same set of tests the following year. The tests can’t have gone too bad, as two years later the upgraded RBS15 SFIII, a customised RBS15 MkII, was introduced in Finnish service as the MTO 85M.

Now the RBS15 is a hot topic again for Finland. The anti-ship missile is one of the candidates for the PTO2020-program, the current acquisition to replace the MTO 85M on the Hamina-class following their ongoing MLU and in the truckmounted batteries, as well as becoming the main surface-to-surface weapon for the new Pohjanmaa-class corvettes (Squadron 2020). And Saab is confident that the RBS15 will be a prime candidate this time as well.

Saab has two distinct versions on the table. Noting that the baseline version was nearing the end of its life, Saab embarked on an ambitious upgrade program. While the step from MkI to MkII was an upgrade, the Mk3 was a radical redesign resulting in what was basically a completely new missile. Following a four-year test program it was adopted by the German Navy, and shortly after that by the Poles. The Swedish Navy is still soldiering on with the MkII, and would have been happy to adopt the Mk3. However, the Swedish Air Force had other thoughts, and had a requirement for the weapon to be lighter to allow four missiles to be carried simultaneously by the upcoming 39E Gripen. The result was the RBS15 ‘Next Generation’ (still lacking an official designation, though Mk4 wouldn’t come as a surprise), which is an upgraded Mk3 with a lighter launch weight, longer range, and generally improved performance. The weapon is contracted for introduction into Swedish service for both the Navy and the Air Force during the next decade, and Saab doesn’t mince words: “It is the most capable and advanced anti-ship missile on the market”, as was explained to us during a briefing.

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The new launch tubes for the RBS15 Mk3 are seemingly of a more complex shape than the older ones, but under the surface ease of manufacture actually means they are cheaper. Source: Own picture

The new launchers are a chapter for themselves, with the original box-like launcher having been replaced by octagonal tubes. The reason behind this is cost-savings, as the original box held the missile tilted 45° to one side, meaning that the railings holding the missile inside the box have very demanding tolerances. The newer launch tube instead holds the missile level, which is somewhat more forgiving on the structures. But it in turn leads to new questions. “The Visby-class will fit the NG, but we have already cut square holes in the side for the MkII, so in that case we will use the old launcher,” a technical sales support engineer explained. “The missile itself doesn’t really care, it can handle both positions.”

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The humble MSU (Missile switching unit) is the only major piece of hardware except the launch container that is needed aboard a vessel to be able to fire RBS15. Source: Own picture

What then is so special about the RBS15? From a Finnish standpoint, the Baltic Sea as the design environment of choice is interesting. The often poor weather combined with a cluttered archipelago and lots of civilian traffic makes for a challenging battlefield, and Saab is one of very few companies designing their anti-ship missiles from the outset for littoral waters as opposed to the open sea. This is also where ELSI comes into play. allowing for advanced simulations of the performance of the seeker, something which plays a key role in evaluating parameters such as ECCM and target discrimination. The weapon is also capable of performing the land-attack role against ‘soft’ targets, though it is not optimised for the role in the same way as ‘true’ land-attack cruise missiles.

The ships we are firing against are not that keen on being hit.

The flight path of the missile is guided through a number of pre-set 3D waypoints, and the missile then navigates using both GPS and inertial navigation to make sure it hits all waypoints on time. Timing is key for features such as simultaneous time-on-target, a default feature for the RBS15, and as such the missile will throttle up and down in flight as needed to hit all waypoints on the exact time given. The exact height of the sea-skimming part of the trajectory also varies according to sea state, with larger waves naturally forcing the missile to fly at higher altitude. And in case the missile misses its target, it will swing around and do a reattack. If no target is found at all, it will eventually head off to a pre-set destruction point, which can be altered by the operator to make sure the missile doesn’t fly off and self-destruct over the nearest town.

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Saab’s technology demonstrator 39-7 displaying the capability to carry two RBS15 under each wing, giving a four-ship of Gripen E an almost unrivalled firepower against enemy shipping. A full salvo will be devastating against enemy warships, but also comes at a hefty price. Picture courtesy of Saab Ab

For PTO2020, Saab hasn’t offered a specific variant, but instead opened the shop and described the Mk3 available today and the NG available tomorrow. The systems will also be interoperable, with NG launchers able to fire Mk3 and Mk3 launchers able (after a software update) to launch NG missiles. Customisation, as has been the case with the earlier Finnish versions, is also an option, but Saab notes that less and less countries are willing to pay the premium of having a customised missile. From a Finnish perspective, the supply chain is interesting. Diehl in Germany handles final assembly, with Saab building many major subassemblies and handling much of the development work and testing in Linköping. However, a new location on the map is Saab’s brand new technology centre, the STC, in Tampere, which is heavily involved in the electronic warfare side of the technology for the RBS15 NG.

The first draft of the text and pictures has been provided to Saab for screening to ensure that no classified, export controlled, or company confidential information is included.