The Siorc-class Diesel-Electric Submarine, or Pattern F-106, is one of the first submarines built by SDY, and in the Free Lands for that matter, in series, following a request for development by the SDF-Navy.

Specifically designed to counter nuclear-powered submarines, the Siorc-class Diesel-Electric Submarine is equipped with the most modern technologies in detection and avoiding detection, as well as computing of the collected data to the end of destroying the enemy while remaining undetected.

The term siorc means shark.


The Siorc-class Diesel-Electric Submarine is constructed using non-magnetic materials, namely special titanium-alloys, whenever feasible and has a teardrop shaped hull for increased sub-surface performance. Sadly, this increased performance below the surface does not translate into an increased performance above the surface, where the vessel is considerably slower then below the surface. The hull is plated with rubber tiles, which further reduce the acoustic signature.

This increased sub-surface performance does not only mean speed, however, but also a decreased acoustic signature, which means a lower likelihood of being detected. Steering is handled by two diveplanes on the sail, which assist with the rising and diving of the submarine together with the ballast tanks, while four rudders, arranged in cruciform behind the singular shaft move the plane to port and starboard.

Communications are handled via several masts, which can be extended out of the sail and back into it as needed or as surfaced, which includes a mast for GPS. A small Nuacht N-35 Mark III Submarine Navigation Radar Mast is used as a Navigation Radar, but can only be used on the surface.

On the topics of communications, which is generally very complicated to arrange with a submerged submarine, the Siorc-class Diesel-Electric Submarine carries a small buoy on a cable with a Very-Low Frequency receptor. The bandwidth between 3 and 30 kilohertz can penetrate water to some very short extend, but, due to the size VLF-Senders need, the submarine can only receive such signals and not send – a transmitter site is needed to sent messages.


The Siorc-class Diesel-Electric Submarine is primarily powered by two Diesel-Electric Engines, which rest on shock-absorbers to reduce the noise of their operation, powering all electrical systems onboard the vessel, mainly however the engines power the one shaft driving the submarine forwards.

In addition to that, for silent running, the Siorc-class Diesel-Electric Submarine is equipped with four Alpha-Type Stirling Engines. Heat for this type of engine is generated by burning the same diesel with an oxidizer, usually liquid oxygen, which enhances the heat output of the diesel and thus allows the engines to generate power at a noise level far below that of the diesel generators.

While the Stirling Engines can only produce a fraction of the power the Diesel-Electric Engines can, thus resulting in for example a much lower speed when only using the Stirling Engines to power the submarine, they are next to absolutely silent.

In total, all engines combined, can produce up to 6,000 kW of energy, which allow the Siorc-class Diesel-Electric Submarine to travel at 13 knots, or 24 km/h, when surfaced, submerged at 20 knots, or 37 km/h, and 5 knots, or 9.3 km/h, on the Stirling Engines alone. The Siorc-class Diesel-Electric Submarine is estimated to have a range of 6,100 nautical miles, or 11,300 kilometres, on the Stirling Engines and can stay underwater for at least two weeks before needing to surface.

Sensors and Processing Systems

The Siorc-class Diesel-Electric Submarine is equipped with a highly advanced sonar suite, comprised of five arrays, one on the bow and four on the flanks. These arrays can be used in active and passive modes, either listening to emissions from other vessels, both on the surface and below, or sending out emissions themselves while listening. Due to their extremely sensitive structure and architecture, these arrays can detect smallest of noise emissions from miles away and also feature a torpedo alert.

In addition to that, the Siorc-class Diesel-Electric Submarine can deploy a Towed-Array Sonar with many of the same characteristics.

For the detection of the radiation emissions of nuclear-powered vessels, and despite any assurances of the producers, there are emissions, the Siorc-class Diesel-Electric Submarine carries a Geiger Counter Array, which analyses the radiation around the submarine and assigns it to sources of radiation, determining the origin, thus finding out, whether or not there are enemy nuclear powered vessels, be they other submarines or surface vessels, in the general area.

Electronic Warfare and Decoys

The Siorc-class Diesel-Electric Submarine is equipped with a suite of Electronic Support Measures, ESM for short, which allow to detect, intercept, identify, record and locate electromagnetic energy, for example radar, and be used to draw conclusions based on these data for operational planning, tactical decisions and other purposes. ESM, however, does not mean deciphering enemy transmissions. Part of this suite is a Radar Warning Receiver, which tells the submarine when it has been spotted by radar.

In addition to that, the Siorc-class Diesel-Electric Submarine carries six launchers for acoustic decoys, which can be used to throw enemy units and torpedoes off the submarine's track. Basically noisemakers, these decoys lure sonars into believing, that the submarine is where the decoy is and not where it actually is.


The Siorc-class Diesel-Electric Submarine is armed with six 533 millimetre torpedo tubes, capable of being loaded with torpedoes, missilesm unmanned underwater vehicles, usually of the wire-guided variant, and be used by frogmen as an exit.

SDY already tested Type 40 and Type 43 Anti-Ship Missiles and Type 50 Cruise Missiles with these tubes, resulting in positive tests. Depending on the exact loadout, the Siorc-class Diesel-Electric Submarine can carry up to 36 shots, six of which are already in the tubes.

In addition to that, the Siorc-class Diesel-Electric Submarine can be used to deploy mines.


Contrary to popular belief, there had been submarines built by SDY before: From a number of prototypes and design studies to a series of research submarines and even a submarine yacht, the Bradaí, as well as a few conversions, we gathered quite an experience.

None of those designed for military service ever really took off or was produced in larger quantities, neither for the SDF nor for export customers. Yard 15 still had a number of submarine construction experts on staff for exactly that reason.

But all of that changed with the Battle of Marley Bay, when the SDF suffered catastrophic losses at the hands of the enemy. In the Naval Expansion Programme of 2013, the development of a number of submarine types was contracted to SDY and other shipyards in the Free Lands in order to give the SDF weapons, which they could use to defend the Lands and their political interests abroad.

From 2013 to 2015, several lists of requirements were made and several designs to match them, with Patterns F-100, F-106 and F-109 being finally selected (F stands for fomhuireán or submarine) by the SDF with Patterns F-105 and F-110 continued by SDY for the export market.

Pattern F-106 would become the Siorc-class Diesel-Electric Submarine, with the first unit, SDFS F-16 Siorc, launched in late 2017 and beginning sea trials. She was commissioned in 2019 with several sisters to follow.

The Pattern F-106 is the first submarine constructed in the Free Lands to use an Air-Independent Propulsion System based on a Stirling Engine.

Vessels of the SDF-Navy

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