The American Torpedo Data Computer (TDC)


The advantages that the TDC gave to our submarines is clear in the attack by U.S.S. Tang, O’Kane as skipper, on a convoy approaching Nagasaki with the lights of its industries on the horizon. Tang closed to find two parallel columns of marus just over a mile apart with escorts rushing about the parameter. Tang remained on the surface that let her use her speed and maneuverability plus radar and lookouts to penetrate inside the convoy. On her third try she managed to elude escorts and get inside the convoy settling on a course midway between the two rear marus. Using the torpedo bearing transmitter (TBT) on the bridge O’Kane sent the bearing to one of the furthest marus to the TDC officer in the conning tower below, who cranked it into the TDC. Next O’Kane called down the angle-on-the-bow that was cranked into the TDC. These two angles were solved by the TDC to show the course of that maru relative to the Tang. The radar man gave the exact range and speed that was cranked into the TDC. When the ready light came on, the TDC had put that information into each of the ten torpedos in its tube, and O’Kane fired three. “Check fire!” He repeated the bearing on a nearer maru, then the angle-on-the-bow, radar added range and speed, and another three fish left the Tang. Now all six bow torpedoes rushed toward two targets, and exploded almost simultaneously, since O'Kane fired at the more distant target first. This made it hard for the escorts to know where the attacker was. O’Kane and two sharp-eyed lookouts watched ships moving until they saw an opening and steered Tang at high speed out of the center of the convoy and into open seas.

Without changing course, the Tang fired torpedoes at two widely spaced targets. The submarines of other nations had to twist and turn to aim the bow at each successive target before firing, being sure to “lead” the target enough for its speed. All these the TDC did quickly and accurately. The TDC was a major advantage used by American submarines in their surface and underwater attacks.

One final event. As Tang raced away from exploding, burning marus, one escort followed. Then a powerful searchlight illuminated the bridge like high noon. Tang dived urgently, preparing for the depth charging they knew they so richly deserved. The escort raced past overhead, while Tang's crewmen looked at each other amazed. Tang had a new camouflage paint job of haze gray with white that had hidden other subs. Every one on Tang knew that paint job had now worked for them. This attack in much fuller detail is told by O'Kane himself in his Clear the Bridge! on pages 221–229.

In one of my seminars a participant was a Fire Controlman in a submarine with the responsibility to maintain the TDC. He said inside was an amazing assortment of cams and gears that he had to keep in perfect alignment. That was an analog computer!