This article discusses some techniques for recreating various aspects of the WWII antisubmarine warfare (ASW) actions that were an integral part of the war at sea in all theaters of operations. Several of the WNII naval rule systems (e.g. see the rules reviews in COURIER II-6) have rules for submarines, but they generally leave much to the imagination when it comes to implementing them in a game. Thus, WWII naval miniatures engagements are almost invariably surface actions.

It is clear why many WWII miniatures rules either ignore submarines or give short shrift to the possibilities of ASW actions. There was always a certain amount of chance element in any ship versus submarine encounter. Even if a submarine was lying in wait on the basis of good intelligence analysis and evaluation, it was possible to miss an intercept by a few mites as the result of relatively small course or speed variations in the prospective target. If the sub was slightly out of position, the submarine skipper often watched helplessly as the target disappeared over the horizon, since the speed advantage was almost always in favor of the surface ship.

Even at night, with the submarine on the surface, it might take hours for the sub to do an "end-around-run" in order to get into a favorable attack position. Thus, if gamers decide that they wish to include submarines, the scenario should be arranged so that an intercepts feasible. Figure l illustrates the region in which a submarine must be located in order to be able to launch an attack. The radius of the torpedo danger zone (TDZ) is the maximum range at which the sub skipper might fire his torpedo with some prospect for success (e.g., 4000-5000 yards). Actually, most skippers tried to be within about 2000-2500 yards before firing (in spite of the published range capabilities of the various torpedo models). The limiting approach angle, Laa, bounds the region in which the submarine can successfully maneuver to fire, based on the relative speeds of the sub and target:

The sub speed might be 3-5 knots (more, if on the surface), the target speed for a convoy, 6-10 knots, and the speed of a naval vessel or task group, 15-20 knots. It is easy to see From the above numbers why some of the liners used as troop transports, like the "Queen Mary", could travel independently in relative safety, if they could steam at 25-30 knots. Scenarios that are to involve submarines need to be planned so that the sub(s) will be within the shaded approach area shown on the diagram. Convoys should be deployed as illustrated in Figure 2. A typical task group formation is shown in Figure 3. Ships in the ASW screen should be spaced according to the SONAR range capabilities for a particular period of the war being depicted, provided there are sufficient units available. Since the entire convoy or task group covers such a large area, one might plan a scenario involving only the screening units or a couple of screening units that are detached to investigate an aircraft sighting or a radio intercept.

Time and Distance Scales

The selection of a distance scale for a naval game is always a compromise between the desire for realism (i.e. game scale = model scale), which requires a lot of playing area; and a compressed scale (i.e., game scale < model scale) to fit an engagement into the space available. A game scale of about one-half the model scale seems to work reasonably well for ASW. That is, for 1:2400 models (16 inches per 1000 yards), a scale of about 7.5 inches per 1000 yards works nicely. The time scale should be in the range of 30 seconds to two minutes per turn in order to provide a reasonable simulation of events.

Hidden Movement

Hidden movement for the submarine is essential. Players or referees can decide whether or not to limit the visual information that is available to the submarine commander. His limits of movement are such that total intelligence (albeit unrealistic) may not make much of a difference, and he is not exiled from the camaraderie of the game. Players can conveniently implement hidden movement for both sides by using a gridded playing area that facilitates placing, removing, and replacing sighted (or detected) units. Off-board movement can be accomplished by using coordinate paper that is keyed to the coordinate grid. A sewing pattern cutting board provides a convenient, ready-made grid of one-inch squares. Since it may be inconvenient to keep shifting detected/undetected surface units on and off the board, covering undetected or un-sighted units with paper or a marker and leaving them in place until detected again will generally provide a sufficient degree of limited intelligence. It will generally be difficult for the sub skipper to estimate intercept conditions for such ships, even if he is tempted to shoot at such "unseen" targets.

The gridded board also facilitates carrying out detection or sighting procedures involving various sensor capabilities (i.e., visual, SONAR, RADAR, MAD, etc.), without a lot of tape measurements. The fact that the units are physically located on a grid instead of an unmarked "ocean" is a minor matter (except in range estimation game systems). After all, ships and submarines had various manual or automatic plots (such as the dead-reckoning tracer) and analog or manual calculation procedures (such as the torpedo data computer or maneuvering board) to keep track of the locations of potential targets.

One aspect that is frequently neglected by ASW rules is the importance of an attack in the general vicinity of an un-sighted sub or on the site of a lost contact. These attacks may be termed "hasty", "urgent", or "pinning" attacks and are made for the purpose of inhibiting the submarine from firing. It was often as important to keep the submarine occupied and ineffective (while the potential targets steamed away) as it was to sink the submarine. One of the benefits of aircraft escorts was to keep the submarines submerged and prevent them from maneuvering into the approach zone in Figure 1.

ASW Attacks

Many ASW missions started with a RADAR contact, a visual sighting of the sub on the surface in the distance, or an HF/DF (high frequency radio direction finder) bearing. The escort would turn toward the contact bearing and head for the target {or suspected target) at high speed. As the escort approached the target location (within 1000-3000 yards), the unit would slow to fifteen knots and begin a SONAR search if a course and speed had been estimated for the target, the attacker would turn to a course on a bearing that would intercept the estimated target track. Once SONAR contact was made, the attacker would turn to a course leading the target bearing and designed to place the depth charge firing pattern slightly ahead of the location of the submarine. During the final stages of the attack the SONAR would lose contact at a range that depended on the depth of the target. Thus, with older SONAR, there was no target information during the most critical moments (unless the operator heard propeller noises as the escort passed ahead of the sub and before the depth charges exploded). If the submarine turned toward or away from the attacking vessel at the right moment, the attack might be unsuccessful even if the attacker detected a maneuver, the submarine could often turn with a smaller radius than the attacker.

The attacker crossed the projected path of the sub, fired the depth charge pattern, reversed course, and attempted to regain contact through the disturbed water created by the depth charge pattern, and, probably, through water disturbed by the attacker's own wake. A SONAR attack from about 2500 yards at fifteen knots would take about five minutes (about 3-8 game turns, depending on the rules used). Since information was transmitted verbally from the SONAR operator to the ASW officer, and since orders were transmitted verbally from the ASW officer to the helm and depth charge crews, attacks were conducted by doctrine and instinct (sharpened by training and experience). There was no time for lengthy evaluations of alternatives or complex ship maneuvers to compensate for faulty judgment.

The ASW officer did have a primitive (but effective) computer in the form of a range recorder that could give him a good estimate of the time to fire based on the closing range rate. He had some idea about the depth of the submarine from the range at lost contact. He also had clues about the aspect or orientation of the target by comparing the pitch of the reverberations from transmitted "ping" with the pitch of the returning echoes. Up Doppler, or higher pitch echoes, indicated that the sub was headed toward the attacker. No Doppler indicated a beam aspect with the sub crossing the track of the escort. Down Doppler, a lower pitch echo, indicated that the target was moving away from the escort (even if the range was closing).

Ahead thrown weapons (ATW), such as the mousetrap and hedgehog, were developed to improve chances for success by being able to maintain SONAR contact throughout an attack. Mousetrap was a rocket-powered projectile that was launched from rails mounted on small vessels and did not require a heavy foundation. Hedgehog was a type of mortar projectile that required space and a gun mount type of foundation. Both missile warheads were similar. They were smaller than depth charges, streamlined, about 7.2" in diameter, and only exploded on contact with a solid object such as a submarine hull or the sea bottom. The smaller size and streamlining meant that the missiles sank more rapidly than a depth charge. If they missed, there were no large explosions to churn the water and inhibit reestablishing SONAR contact. The ATW had a range of 200-300 yards and were fired directly ahead of the attacking vessel.

Thus, it was possible to maintain contact throughout the attack and corm the ship after firing in a manner that would maintain contact through the next run. The mousetrap pattern generally consisted of one or two lines of eight charges laid perpendicular to the course of the sub. The hedgehog pattern was 24 charges on the periphery of a circle or oval approximately 150-200 feet across, depending on the model of the weapon. Mousetrap was aimed by turning the vessel. Hedgehog had a limited azimuth training capability by tilting the spigots on which the mortar shells were loaded.

Tactics were also developed for coordinated attacks by two or more ships. One ship was maneuvered on a course and speed that was roughly parallel to the submarine track and located so as to maintain continuous SONAR contact throughout a series of attacks by the other vessel(s). The other ship(s) did not use SONAR, but were vectored over the target and told when to fire by the coordinating ship. This procedure had a number of advantages in addition to the continuous contact. The submarine was denied the usual cues that sometimes helped evade a normal attack.

The range to the coordinating ship would not change very much. Thus, the sub would hear the SONAR pinging in a search mode instead of shifting to a more frequent pinging during the attack. The attacking vessel might attack at 8 or 10 knots, instead of 12-15 knots. Thus, the attacking ship would be quieter and the enemy either might not hear the attacking vessel or might assume from the slow propeller beat that it was just searching. The pinging from a single ship avoided SONAN interference and kept the target in doubt as to how many ships were attacking.

Submarine Countermeasures

In addition to stealth, changing depth, and maneuvering, submarines had some additional countermeasures. Some German ships were "painted" with a rubbery coating to absorb the acoustic energy and reduce the strength of the SONAR echo. One occasionally sees wartime pictures of these subs, which had a kind of shaggy appearance, as the coating did not adhere very well. A very sharp turn would produce a vortex or whirlpool in the water called a "knuckle". The knuckle provided a body of water with different characteristics that often returned an echo something like a submarine although the range was not as cleanly defined as the sharp hull echo, and it had no Doppler.

In addition, if the sub withdrew behind the knuckle, the SONAR signals would generally not penetrate the disturbed water. The Germans developed a device called the "pillen werfer" that launched a kind of giant "Alka-Seltzer" tablet that produced a heavy bubble screen. The "pillen werfer" could be used as a decoy or as a screen like the knuckle. An active and effective countermeasure was the acoustic homing torpedo that blew the sterns or propellers off numerous ships before a counter-measure was developed. The surface ship counter measure was the Foxer (FXR) noisemaker that was used to decoy the acoustic torpedo and, explode it at a safe distance astern of the ship.

The addition of submarine and ASW actions represents a whole new spectrum of activities to enhance the excitement of traditional naval miniatures engagements. I hope that some of the ideas may be of interest to the reader.

BIBLIOGRAPHY

Beach, Cdr. Edward, Submarine, Signet Books (1953)
Blair, Clay, Silent Victory: The U.S. Submarine War Against Japan, Volumes 1 and 2, J.B. Lippincott Co. (1975)
Chambliss, Wm.,The Silent Service, Signet Books (1959)
Hodges and Friedman, Destroyer Weapons of World War 2, United States Naval Institute (1979)
Hughes and Costello, The Battle of the Atlantic, Dial Press (1977)
Macintyre, Capt. Donald, U-Boat Killer, Avon Publications (1956)
Mason, David, U-Boat: The Secret Menace, Ballantine Books (1968)
Roscoe, Theodore, United States Destroyer Operations in WWII, United States Naval Institute (1953)
Roscoe, Theodore, United States Submarine Operations in WWII, United States Naval Institute (1949)

ASW Charts (slow: 162K)