Transferring reality to a board game

THEY COME UNSEEN isn’t a simulation but rather uses actions that have an authentic background in keeping with the theme; submarine warfare and anti-submarine warfare (ASW) are complex subjects simplified to bring them to life as a family board game. This page explains how real-life has been conceptualised for a cardboard world.


For most forms of motive power, in order to achieve greater speed, greater amounts of energy or fuel are required and expended. 


In THEY COME UNSEEN playing pieces move diagonally and orthogonally across a square grid on the two playing boards.  The maximum number of squares that a submarine or ship is allowed to move at any particular stage of the game is based on the “speed” of that vessel during an equal, finite, fixed and yet undefined period of time (a vessel’s move or turn).  A vessel’s “speed” is therefore dependent on the number of squares that it moves during a ship's turn and will have operational implications for that vessel.

Photo credit: Commodore M.D. Macpherson Royal Navy: Leander class frigate charging (COQC 1980)

A periscope view of a Leander class frigate at 30kts - THEY COME UNSEEN | Concepts

For example: destroyer ‘A’ moving 18 squares covers a greater distance during its move than destroyer ‘B’ moving 6 squares in the same equal, fixed and finite time (a turn).  Destroyer ‘A’ was therefore moving at a greater “speed” than destroyer ‘B’ to cover the greater distance in the same time period and the operational consequence of using greater “speed” is higher fuel usage; a destroyer that splits a move into two or more phases to conduct various activities will also pay a slight fuel usage penalty compared to if it was just making a straight run (the one fuel efficient exception for destroyers is when conducting the 4-square RAS move with the supply ship for which, for simplicity, there is no fuel penalty).  For all the surface ships, increasing speed increases noise output as far as acoustic mine activation is concerned; noise reduction techniques applied to warships will delay the point at which a triggering noise level is reached.  Finally, increasing wave height will reduce a ship’s maximum achievable “speed” as it struggles to punch its way through the mounting seas (the "Weather" mechanic).

The same principle of “speed” also applies to submarines.  As well as an overall maximum “speed”, limited in real life by the available power reserve in the storage batteries and drag on the hull, casing and fin, submarines have a lower maximum “speed” imposed on them in the game (6 squares) during moves that include squares in SHALLOW water (250 feet).  Submarines move in three dimensions and away from the gaming table operate within a “manoeuvring envelope” that provides maximum recommended speeds for given operating depths and depths of water; these limits are recommended in order to manage the risk, in the event of a mechanical or electrical failure to the hydroplanes (a submarine’s control surfaces), of inadvertently broaching at the surface, exceeding pressure hull crush depth in very deep water, or thumping into the sea-bed in water shallower than hull crush depth.  Submarines change depth by angling the hull upwards or downwards through the movement of hydroplanes fitted near the bow and stern and driving themselves shallower or deeper.  At high speed the movement of the hydroplanes, near the stern in particular, have a greater and swifter effect on the bow up or bow down angle of the submarine than when moving slowly through the water. The “Manoeuvring Envelope” is a safety concept that was introduced in nuclear powered submarines because of their high underwater speeds which magnify the effects of hydroplane failures, giving less time for the control room team to react to the emergency; the necessary guidance for speed versus depth is obtained from a “Manoeuvring Slide Rule”.  For conventional submarines c1960 these safety margins were less critical owing to lower underwater speeds and so it was more a case of operating “by the seat of one’s pants”, but the logic still applied and so use of slow speed in shallow water has been translated across to the rules of the game.  Apart from that, submarines are for the most part blissfully unaffected by sea conditions such as wave height ... but it can become too rough to snort.


One of a submariner’s foes is the anti-submarine warship; a fast, manoeuvrable vessel equipped with search and attack active sonars and anti-submarine weapons; in the 1960s these weapons would be relatively short range requiring the ship to manoeuvre close to the target submarine in order to attack.


The primary location device used by anti-submarine warships is active sonar; this transmits high energy pulses of sound through the sea to bounce back off a submerged object providing a returning echo that the warship can receive and display.  Systems will have search and attack modes or have separate sonars for each role. 


Sonars of the era in favourable conditions, and on a good day, could provide information about a submerged target’s position and, with tracking, its movement as well as an assessment of the target’s depth. However, it's not always that straightforward.  The prevailing sea conditions (surface & sub-surface) and water depth, the relative bearing of the submarine from the searching ship and the aspect presented by the submarine to the sonar transmissions can all affect the quality and strength of the returning echo and so the act of searching for and tracking a submarine is fraught with difficulties.  In addition, all active sonars have a 'dead range" (Dead Range: a range inside which an echo cannot be received because the sonar is still transmitting the outgoing pulse into the sea).

Photo credit: Commodore M.D. Macpherson Royal Navy: Type 21 frigate at speed (COQC 1980)

A periscope view of a Royal Navy Type 21 frigate at speed - THEY COME UNSEEN | Concepts
A Soviet destroyer conducting an active sonar search during the board game THEY COME UNSEEN

The active sonar searches used in THEY COME UNSEEN attempt to convey these difficulties by the use of imprecise search sectors of 9 squares forward of the beam (most accurate) and 12 squares abaft the beam (least accurate) as well as the presence of a blind arc created between the sonar search templates. These elements combine to provide interesting restrictions for the destroyer captains to manage and for the submarines to exploit while demonstrating that obtaining and maintaining contact on a submarine doesn't always go as planned!  [The limit of one search per destroyer per turn is to provide balance.]


Reality isn’t turn-based and in the field of anti-submarine warfare an active sonar search could be conducted continuously and all valid contacts could be prosecuted and attacked.  In a turn-based game the continuity of a constant real-life search would be lost if the ability to search ended at the end of a player’s turn, allowing the opposition to get away undetected if close by.  The SONAR WATCH mechanism is designed to bridge this gap between successive Soviet turns by enabling detections (but not attacks*) to be made on submarines should they pass through the sea area covered by the sonar templates during NATO’s turn.  [*The restriction on attacks in this context, and in other aspects of the game, is to provide balance between the two sides].


Having gained contact on a submarine, the short-range anti-submarine weapon systems of the time (1960s) generally consisted of high-explosive depth charges lobbed ballistically into the sea towards a suspected target submarine's position, and set to explode at a pre-set depth or with a proximity fuse. Royal Navy ASW frigates, and frigates of many other Commonwealth navies of the era, had the Anti Submarine Mortar Mk 10 system comprising one or two 360° trainable, three-barrelled mortar tube mountings, mounted near the stern; this was a development of the WW2 Hedgehog and Squid systems. 


(1) HMS TENBY (1969) The after LIMBO mounting with the last tube of the forward mounting just visible on the left.

(2) A Soviet ASW salvo attack of 6 mortar bombs during the game following contact in the starboard forward sonar search sector.

ASW "Limbo" mortar Mk 10 mounting onboard HMS Tenby - THEY COME UNSEEN | Concepts

These fired 180kg (warhead 94kg) anti-submarine mortar bombs in triangular patterns of three or six at ranges of 400 to 1,000 yards from the frigate - a system known as ‘Limbo'.  The Soviet navy used similar ASW weapons and while not identical to ‘Limbo’, the ‘Limbo’ system is the type of weapon that I implemented in THEY COME UNSEEN with each cube representing one ASW mortar bomb.  In the real world, ships could carry up to 17 salvoes; the limit of 3 salvoes imposed in the game is to provide balance, as is the restriction of one attack per turn per submarine detected.


Fundamental to extended operations at sea is the ability for naval forces to replenish food, fuel and weapons on the move.  Manoeuvring in close proximity, replenishment at sea is achieved between warships and a tanker or supply ship all of whom maintain a steady course and speed throughout the operation while connected by a fuelling hose and/or a storing gantry; a procedure requiring high standards of seamanship by all concerned.

Photo: Twitter @RoyalNavy 

Replenishment At Sea (RAS) - THEY COME UNSEEN | Concepts
RAS extract.png

In THEY COME UNSEEN a RAS is achieved by one (or both destroyers with one each side of the Supply Ship) moving in a straight line for 4 squares alongside the Supply Ship (mimicking the need for a steady course & speed for a finite time); the stores transferred are weapons and fuel (for simplicity it is assumed that food stocks are sufficient throughout a game).  Forward planning is required not only to ensure the right stores, and the Supply Ship, are where they are needed at the right time but also that the 4-square move is operationally advantageous in its direction. (There is no fuel penalty for the destroyer(s) during this 4-square move but it is part of their total move allocation as it is for the Supply Ship).


"Snorting" is the Royal Navy term for the process of drawing air into the submarine through a snort (snorkel) induction mast to allow the diesel generators to be run to charge the batteries while at periscope depth (PD); the diesel exhaust gases are led outboard through a snort exhaust mast.

A snort is a fundamental activity for survival in a conventional submarine before the days of Air Independent Propulsion (AIP).  It is the time during an operational patrol when a conventional diesel-electric submarine is at its most vulnerable from seaborne and airborne radar, passive sonar or the “Mark 1” eyeball.  A submarine captain would take his boat to PD to snort as often as the battery state and the operational situation demanded and allowed and would expect to conduct a snort undetected, using electronic support measures (ESM) to detect radar transmissions before they become a threat and by snorting for as short a time as possible to minimise the risk of sonar detection … it is always a balance.  In a particularly hostile radar environment a snort may well be started and stopped many times without achieving a battery charge.  Whatever the outcome, the captain will always want to move away quietly from the "Stop Snorting!" position.


(1) EVERY snort is detected (declared)

(2) EVERY snort achieves a 10 unit increase in battery capacity

(3) after EVERY snort the submarine is limited to moving a maximum of three squares away from the datum piece at the end of the move.

These three factors are included in the rules to help to achieve balance in the game between the two sides.

The photograph below shows HMS GRAMPUS snorting off western Scotland (c1974); I was down there and might even have been on the periscope!  The masts raised are (L to R): search periscope, snort induction mast, wireless mast, and (with its top hidden slightly below the surface) the snort exhaust mast.

[NOTE: This example is a rather non-operational snort taken during aircraft radar trials; the wireless mast wouldn't normally be raised during a snort (it was here to talk to the RAF Nimrod crew taking the photo) and the boat would normally have been moving much slower to both maximise the battery-charging rate and to avoid creating such an obvious wake; also, the underside of the ball of the snort induction mast should be just skimming the surface to reduce detection opportunities. Photo credit: RAF 1974]

HMS GRAMPUS snorting off coast of Scotland - THEY COME UNSEEN | Concepts


A submarine game of course needs to work in three dimensions which is achieved by using two boards and the depth gauges.  In reality a submarine captain can decide to patrol at any depth within his boat’s depth operating limits but to allow this in THEY COME UNSEEN would introduce far too many variables with which the SOVIET team would have to contend!  NATO, therefore, are limited to three specific depths on the DEEP board: 200, 400 and 600 feet; feet are used as the unit of measurement of depth because 'feet' were used throughout my submarine service; depth keeping in metres would come later.  Depth measurement is based on keel depth; a submarine at 200 feet in a water depth of 250 feet is therefore 50 feet clear of the sea bed.  A surfaced submarine would have a keel depth of around 18-20 feet; at periscope depth its keel depth would vary in an approximate range of 50-60 feet.

In THEY COME UNSEEN the NATO submarines either appear on the MAIN board as a Datum piece indicating a snorting move at periscope depth, or as the submarine playing piece to indicate that the submarine is on the surface. For simplicity both situations are interchangeable in the game as far as the depth gauge is concerned and the states can be changed without any movement or a battery penalty; it is simply the use of the different playing pieces that indicate the chosen state of operation: surfaced or snorting on the MAIN board.

Photo credit: RAN 1984: HMAS Oxley

HMAS Oxley receiving visitors - THEY COME UNSEEN | Concepts


Torpedoes were the primary weapon system for submarines in the Cold War era.  In Royal Navy diesel boats an outfit of torpedoes would be embarked: a mix of World War II era diesel-powered torpedoes (the Mk 8 torpedo); newer, wire-guided, electrically-driven torpedoes (the Mk 23 ... and later the Mk 24 Tigerfish) and, for the after tubes, swim-out 'fire and forget' electrically-driven torpedoes (the Mk 20).  


In THEY COME UNSEEN luck and random chance are minimised. I had become frustrated by games in which the roll of dice had more impact on how a game played out than the skill and tactics employed by the players. For this reason my design does not include dice and by doing so the inclusion of a 'torpedo attack effectiveness and damage' mechanic was ruled out on day one. Such a mechanic would require a probability matrix and the random roll of dice to resolve actions.


Mines (the Mk 5 ground mine) could also be carried in the torpedo racks - cylindrical in profile and loaded into the torpedo tubes for discharge. The actuation options for mines were varied: pressure, magnetic influence, noise or a mixture. Laying mines required navigational accuracy of a high order to ensure that friendly forces could be confident about the position of their own minefields; a submarine was ideal for this role, conducting a mine-lay unseen and, hopefully, undisturbed.

Another role for conventional submarines was that of clandestine operations. landing small parties of troops. Commandos could be carried submerged to close inshore before, under the cover of darkness, the submarine surfaced partially and the canoes or inflatable boats were assembled on the casing before the submarine dived from under them. The canoes or inflatables could then snag a tow rope around a raised periscope 

and be towed further inshore until the point where the submarine needed to withdraw and the periscope would be lowered, slipping the tow. Recovery after the operation could be achieved by running aground on the 

submarine's casing as it came awash during surfacing - an exhilarating experience I gained first hand as a Midshipman when serving in HMS Finwhale in the Far East in 1970. 

So, instead of torpedoes these other realistic forms of submarine-based aggression were implemented both of which could be included satisfactorily in the gameplay without any need for probability resolution. 


(1) Laying minefields (these minefields last for the duration of the game and can achieve multiple hits on unwary seafarers. Rule book page 9: Once laid a minefield remains active for the entire game.)#


(2) Landing commando forces to destroy fuel & weapon installations and any vessels alongside.


# All modern submarines can deploy mines - specialist minelaying submarines were not a feature of the Cold War. Specifically designed minelayer submarines existed during WW2 because of the type of mines available to deploy ... buoyant, horn-contact mines tethered to the seabed by weights ... which had to be stored outside the boat under the casing and deployed over the stern from rails. Modern mines are cylindrical and are laid by discharge from the torpedo tubes. I conducted several (practice) minelays from submarines during my career (as well as special forces insertions against land targets ) - just two of a submarine’s many roles. 


The environmental conditions above, on and below the surface of the sea will influence the tactics employed by ASW warships and by submarines.

Above the surface the general weather patterns can be both predictable and following a general pattern as well as unpredictable and variable (for simplicity in THEY COME UNSEEN they are predictable and follow a general pattern across the three weather areas: WEST, CENTRAL & EAST).  Strong winds blowing across wide expanses of the seas (the "Fetch") can lead to mountainous seas which impose far greater restrictions upon surface ship operations than they do for submarines.  With increasing sea state the comfort and efficiency of surface ship crews can reduce as can the efficiency and effectiveness of their sensors and weapon systems which can necessitate a reduction in speed to achieve the best results unless other priorities exist.  In THEY COME UNSEEN, the weather mechanic of six storm levels provides a predictable and gradually worsening weather regime with a 3-step lull between each brewing storm ... life at sea is challenging!


Below the surface the strength of the wind will create stirring of the subsurface environment which for the submariner is very much affected by the physics and chemistry of sea water. The size of the waves and swell will hamper operations at periscope depth - and in THEY COME UNSEEN at Storm Level 6 the sea state is too rough to snort - but it is the subsurface factors that are more important.  While these factors have an effect on the trim of a submarine they also importantly affect the propagation of sound through the sea.

An Oberon class submarine's "Snorting barometer" - THEY COME UNSEEN | Concepts

A SNORTING BAROMETER.  Measuring the pressure inside the boat, snorting must be stopped if the needle is continuously in the YELLOW or as soon as it enters the RED.  The needle would regularly enter the YELLOW sector as waves passed over the float head valve .. deciding the point at which it was 'continuously in the YELLOW' was very much a "finger in the wind" & 'pressure on the ears" decision.

Photo credit: HMCS Ojibwa Museum, Canada

Sound velocity and sea water density depend on temperature, salinity and pressure (depth); an increase of temperature, salinity or pressure will cause an increase in sound velocity. Temperature is the most variable of these and has the greatest effect on sound velocity causing the refraction of sound pulses from a straight line path. Sound travels faster where its velocity is high (in warm water) and bends towards the depth where sound velocity is lower (in colder water) with the result that the sound's path is refracted. The boundary where this change occurs markedly is known as layer depth; the layer is the body of water above the boundary and layer depth is the depth of the boundary. This refraction can bend sound pulses away from a target that could otherwise have been detected. Submarines and ASW warships can deploy probes to discover the temperature gradient in the sea, and the layer depth if it is present, in the operational zone. Submarines can also check for the presence of a thermocline using a sensor fitted to the hull that records sound velocity as the submarine moves up and down through the sea, although this limits investigation to within the vessel's operational depth limits. Effective use of a thermocline and of the layer depth can enable a submarine to remain undetected by active sonar.  In reality thermoclines are temporary and variable but in THEY COME UNSEEN two layers are deemed to be present; one in Storm Level 5 (layer at 300 feet) and the other in Storm level 6 (layer at 500 feet) with submarines below the respective layers being undetectable by the active sonar search templates ... features for all the protagonists to master.

The operational and tactical challenges that a layer presents to searching warships later led to the development of Variable Depth Sonar, towed behind a warship and lowered beneath the layer, and to sonar lowered below a hovering helicopter armed with homing torpedoes. Both these advances postdate the setting for THEY COME UNSEEN.