Dr. Edward is the Director of the Submarine Research Center (SRC). He holds a bachelor’s degree from Occidental College and a doctorate from University of Sonthem California. He qualified as an enlisted man STERLET (SS-392) SIRAGO (SS-485) and served on the SubPac staff and IV AHOO (SS-565).
Mr. Michael Green is one of the country ‘s leading ex- pert tank technology and tank history’. He is the spokes- person for the Little field Tank Restoration Facility in Santa Clara, CA and author of several books on tank development The Tiger Tank at War, The Sherman at War and The Panther at War, all published by Zenith Press.
Tanks and submarines have a few common characteristics. They arc mobile weapon platforms that encapsulate their crews. Their missions arc to destroy their opposite number in the enemy’s arsenal as well as crippling other enemy valuables. Their dissimilarities outnumber their commonalities by virtue of their operational environments and discrepant motion patterns. During the Second World War, these differences manifested themselves in dissimilar tire control methods.
The United States produced the M4 series of Sherman tanks in great quantity. It was classified as a medium tank because of its weight and had limitations that have been described elsewhere in detail. Many of the tank’s shortcomings were corrected during the war, including the improvement of its 75 mm cannon. In making improvements to the tank’s fire control, the Army found that, as telescopes and periscopes became more complicated, operational reliability was reduced. For that reason it built into its tanks a redundancy of fire control sighting equipment. For example the Sherman tank commander had a vane type sight mounted on the turret top in addition to its telescopic gun sight and periscope. 1 This could be used when the gunner’s optics were knocked out of alignment. The German Panzer IV medium tank used a bar sight as back up.
Tanks were equipped with a coaxial machine gun. It was exactly parallel to the cannon and was used to lay the cannon onto a target. The gunner fired the machine gun and when the tracer bullets were observed to strike the target the cannon was fired. This practical approach to fire control accuracy had the obvious drawback of revealing the location of the firing tank. Nevertheless, it was a primary method of gaining an accurate range.
Submarine fire control methodology consisted of solving mathematical problems in the sinking of ships, while tank crews relied on the commander’s spontaneous ability to determine range and azimuth. 2 A submarine’s water environment required it to accurately define its own motion and that of the target. The captain and fire control party visualized the attack situation from the com fort of a quiet and relatively level conning tower.
On the other hand, the commander of a Sherman tank had no such luxury. His tank was equipped with a primitive pitch dampening gyro which was designed to hydraulically maintain cannon stability as the tank bounced over uneven terrain, but the gyro was so unreliable that it was seldom used. Even when the system operated as designed, it only compensated for movement around one axis and as such was of little use. 3 The Germans also unsuccessfully tried to install a stabilizing gyro in its tanks. Second World War tanks could not shoot their cannons with accuracy while moving.
Projectile velocity was produced by expanding gases in a tank’s barrel. The longer the barrel the greater the exiting velocity. German Pander IV and Panther tanks increased the length of cannon barrels from L33 to L44 to L48 and finally to L 70. Medium German tanks were limited to barrel lengths of L48. These had muzzle brakes which helped to dampen the violent recoil. The Sherman’s 75 mm gun was likewise lengthened for greater muzzle velocity. 4 Modifications to the Sherman turret included strengthening gun grunions, installing recoil shock absorbers and adding a travel lock for the barrel. The German Panzer IV’s turret floor had to be modified to allow for full barrel elevation.
Greater muzzle velocity produced longer ranges and medium tanks on both sides increased cannon ranges up to about 2000 yards, although such an extreme distance was achieved at reduced penetration power and accuracy. A Sherman tank commander, seeking to increase his barrel elevation often placed his tank on the rise side of an earth depression. It is interesting to note that the optimum range for a submarine’s torpedo attack was about 1200 yards with most approaches being less that 2500 yards.
Tank battles were fast-paced with repetitive target acquisition requiring furious loading of either HE or AP rounds as determined by the tank commander. Instant reactive response to the tank commander’s orders were required in aiming the cannon on successive targets. While American tank training manuals called for precise phraseology, the tank commander typically used terrain features to guide his gunner onto target. The gunner had the option to use the tank commander’s estimate of range, to use his coaxial machine gun to validate range or to use his gun sight to obtain a range. In practice, he might use all three or any combination .
The Sherman gun sight was a low power telescope (M70F, 3 power, 22 inches in length) with a drum on the side of the telescope mount. By turning the drum the gunner could align range markers (AP on one side of a vertical reticent and HE and on the other side) onto the target image. In so doing, the telescope was moved upward or downward in relation to the cannon barrel. As the telescopic sight was depressed for greater range, the barrel was correspond- ingly elevated. The amount of the barrel’s super elevation deter- mined the ballistic arc of the projectile in flight to the target. Second World War tank fire control methodology has been described as seat-of-the-pants. In contrast, during the same period, United States submarines sank ships using fire control methods that centered on bringing the submarine into firing range so that it could release a torpedo to hit the target at impact point.
Bearings, the line-of-sight direction from the submarine to the target ship, were obtained through the TBT, (Target Bearing Transmitter), when on the surface and periscope when running submerged at periscope depth. Bearings could also be acquired using radar and active sonar; however, enemy ships were normally equipped with electronic emission detection gear and the use of radar/active sonar meant divulging the submarine’s presence. ‘ It chose to emit electronic impulses into the air or water as sparingly as possible. When obtaining target bearings, passive sonar, which detected underwater sound by hydrophones, was normally used without compromising the submarine’s position.
Obtaining bearing information was relatively simple. On the other hand, range information posed a much greater problem. When making a surface approach the experience of the captain in estimating range was the primary source, just as it was with the tank commander. When running submerged, the periscope was used. It was equipped with a diameter which presented a vertical split image of the target. Knowing the height in feet from target waterline to top of masthead, (obtained from a ship-type reference manual), the target split image could be vertically aligned so that the waterline of one image was at the tip of the masthead of the opposite image. The quartermaster could then read the range in yards from a range dial on the opposite side of the periscope. Typically, the quartermaster or a designated officer read relative target bearing from a periscope ring calibrated in degrees, and target range from the stadimeter dial. This information was fed into the Torpedo Data Computer, which mechanically generated a continuous picture of changing submarine motion and target motion.~
The primary weapon used by American submarines was the Mark 14, Mod 3A torpedo. 9 The TDC produced electrical signals through a synchrony-servo system that turned spindle settings in the torpedo. These consisted of running depth, course to the impact point and torpedo speed which could be set at either 30 or 45 knots. Since the range of the torpedo greatly exceeded most firing solution ranges, the normal speed setting was 45 knots.
The essence of the submarine fire control problem was defining the impact point when both submarine and target ship were normally in constant motion. With own-ship (submarine) course and speed entered into the TDC, the problem became one of estimating target speed, from sonar turn-count information and captain’s observations of bow wake, and of estimating target course by the captain’s estimate of target’s angle-on-the-bow or aspect angle. 10 By translating relative bearing to true bearing and knowing the angle-on-the-bow an accurate target course could be entered. It then became a matter of trigonometry. Knowing the distance to the target (leg of a right triangle) and the angle in degrees formed by the target’s track and line-of-sight, an accurate distance to the track could be calculated. Extending the track by knowing the target’s speed, a torpedo course could be determined taking into account the torpedo’s travel before turning and the turning radius of the torpedo.
A critical concept was that when zero torpedo gyro angles were used, (when the submarine’s torpedo tubes were aligned to the impact point as one would shoot a gun) an accurate range became less critical to a hit. Of course, the solution’s weakness lay in the possibility that a target could change course or speed during the torpedo’s run and thereby avoid the impact. Likewise, it could change course at intervals (zig-zagging) which would require the submarine tracking party to restart its problem-solving effort. Submarine fire control techniques tended to be somewhat complicated because nearly all approaches were with large target deflec- tion angles and slow-running torpedoes. This meant large lead angles with less probability of a hit unless the impact point was precisely predicted. The process involved input from several sources: periscope, sonar, TDC and a plotting party that was not in the conning tower and that had all the inputs of the TDC. This party, usually of two or three officers and highly qualified enlisted men, independently ran a geographical plot and acted as a confirmation of data produced by the TDC.
Unlike the tank, the submarine had time on its side. Being the predator, it stalked its prey and often threw in the towel when a correct solution was impossible. It then surfaced, went to flank speed and out ran the target ship to again lie in wait for the ship to cross its path. More than one end-around was sometimes necessary and a single chase might take up to several days. Patience and persistence were the watch-words for successful submarine captains, but it was an exhausting process. Since most target ships were escor1ed by anti submarine escorts, the attack also involved the trauma of repeated depth charge attacks.
The obvious similarity of Second World War tank and submarine attack doctrines was the need for visual contact with the target. If one couldn’t see the enemy it couldn’t he destroyed. This meant that ranges beyond 2000 yards were improbable.’ 1 The nature of the submarine attack was slow, calculating and required great patience. The tank battle could be defined as, kill him before he kills me. The tank crew worked feverishly to find favorable cover, load the proper ordnance and quickly determine the azimuth and range to target. This was repeated many times during a battle.
The one paramount similarity was the claustrophobic environment of tank and submarine. The respective crews depended entirely on their vehicle’s strength, on the reliability of their equipment and the ability of every man working as a member of a team.