German TDC versus US TDC

[Jimbuna]

Based purely on ifo I've read over the years, in 39 the german equipment was better but come 43 and the introduction of the MK IV meant the American version was superior

[P_Funk]

Okay. Then now is when I want to ask: how was it better?

[Hitman]

These nations all developed torpedo fire control computers for calculating torpedo courses to intercept targets, but the TDC added the ability to automatically track the target. The target tracking capabilities of the TDC were unique for submarines during WWII and set the standard for submarine torpedo fire control at that time.

Quoted from your link That's exactly the reason it was superior. All WW2 TDCs were basically angle solvers, i.e. analog "automated" slide rulers, and as such their output was only as good as their input (Your estimates of range, distance, etc.). But the position keeper was different. It made a "prediction" or "simulation" of the targets movements after your inputs, using the speed, course and all data you gave the TDC. This was useful for two reasons:

1.- Being able to fire with no visual reference -i.e. not raising scope necessary- and also staying aware of tactical situation.

2.- Being able to CHECK wether the target actually behaves as it was expected. If the target is really where the TDC predicts it shall be, then you have a really good firing solution.

[P_Funk]

Ah. So the American TDC actively tracks the ship based on the input. Very nifty.

I can dig it.

[Hitman]

Well, not exactly "track" like modern subs do. Tracking as I understand it means that it continuously updates the theoretical position of the enemy with the data it is constantly receiving automatically (No need for crew input except initially assigning the target to an automated "tracker", which will follow it) from sensors like sonar or radar. The WW2 US TDC did not "track" the target in that it did not continuously received updated data -It was manually entered by the crew-, it simply simulated based on the last data entered what the target would be doing if nothing else had changed (Speed/course). You possibly had already understood it, but I just wanted to be more precise, in case it was of interest for you when comparing with modern subs