With modern submarine fire control technology obtaining ranges is greatly simplified. Attack centers now track multiple targets from accurate passive sonar information, but reaching back into history from the Mk 104 fire control system through the Mk 101 system we come to the mechanically driven Mk 3 Torpedo Data Computer. And what a grand old girl she was. Housed in the conning towers of Fleet boats and Guppies, her gears and synchros made a pleasant whirring noise when in operation.

Actually, the TDC was in two sections: the position keeper and the angle solver. The former integrated time and motion into a continuously generated picture of own ship and target. Little arrows indicated the course of the torpedo for a given set up. As inputs were made by the TDC operator from sources such as the captain's periscope observations, bridge TBT (Target Bearing Transmitter) bearings, radar and sonar the solution to the relative motion problem became more accurate.

The angle solver used the information from the position keeper to generate a torpedo gyro angle (torpedo course to the target) and a spread doctrine as defined by the approach officer, normally the captain. The standard 3 torpedo spread was MOT, Aft, Fwd. Electrical impulses traveled to the torpedo tubes and through spindles into the torpedoes. Contrary to movies, it was the quartermaster who actually punched the red firing button after turning the appropriate switches on the torpedo tube-ready indicator panel.

John Wayne was dramatic when he yelled, "Fire" to all those in the conning tower set of, "Operation Pacific." In a real submarine the word fire means "fire", like a blaze with flames and smoke. The use of the word is likely to evoke action from the damage control party. Back up for a moment and visualize the sequence of "firing" a torpedo at a surface target. Assuming that the target ship is closing, the captain tries to bring his boat into a decent firing range; optimal being 1200 yards and maximum being 2500 yards This means jockeying the submarine's speed and course while taking many periscope observations, all which are never more than ten seconds. Each observation obtains, bearing (read from a relative bearing ring at the top of the periscope tube, range from a stadimeter dial on the opposite side of the eye piece and target angle on the bow from the captain's judgment. As each datum is called out, the TDC operator enters the input into the machine by turning small crank handles below the display panel.

When close to the firing point with torpedo tube outer doors open, the tubes to be used lighted on the tube-ready panel and the spread to be used entered into the angle solver, the captain announces in almost a whisper, "Final bearing and shoot." This alerts those in the conning tower that the time has come for the Mk 14/3A torpedoes to be pushed out of the tubes by compressed air. He then lifts his thumb and the quartermaster pushes the lever which brings up the periscope. The assistant approach officer quickly aligns the periscope to the generated bearing and the captain confirms by observation that his solution is correct. He rapidly says, "Bearing, mark. . .range mark . . .angle on the bow port 110. . .down scope" The TDC operator says, "Set." The assistant TDC operator on the angle solver says, "Shoot." and the quartermaster with a stop watch hits the firing button. He flips the switch to the next tube and when the time laps indicates, hits the button again. It's team effort with each person in the conning tower knowing his job and the TDC being the focal point of relative motion visualization.

A few points of contrast need to be made between World War Two submarine movies and real submarines of the time . Conning towers were quiet. They were cramped with equipment and people, so there was no need to shout. No one wore a hat. Least of all, the captain. They would have been a nuisance when trying to use a periscope. Sinking an enemy ship was a mathematical problem requiring trigonometry. It took a lot of thought. Most of time when making an approach there was no talking; only thinking. To get the submarine into firing position meant lots of patience and persistence. The men throughout the submarine at battle stations torpedo fought fatigue as hour after hour dragged by. And all the effort may have been in vain, because the target ship may have altered course away and the submarine's submerged speed wasn't enough to close the range.

Motion pictures are about 120 minutes in length. Most of that time is spent showing the romantic side of dancing at the officers' club. The director has to get the conning tower stuff done in jig time. Up scope, there he is and fire the torpedoes. John Wayne, Glen Ford, William Holden and Clark Gable made excellent skippers and their audiences got the general idea of what is was like in a Fleet Type submarine, but one must take the sequence of action with a grain of salt. Stretch it out over many hours, even days, add the smells of body sweat and diesel fuel and show the sore feet and aching backs of those who man the attack equipment. In the world of movies, accuracy is secondary, drama is critical. In the world of submarines, accuracy is essential, drama is to be avoided.