Historically-Accurate TDC Usage

[Nisgeis]

This is going to be qute random, so apologies for that:

The in game TDC doesn't really match up to a real TDC. In many ways it's a poor version of it, with lots of functionality crippled or missing. The chief crippled feature is the adjustment of the bearing, which messes up the target course, which destroys your whole solution and causes lots of frustration for new users of the TDC.

The real TDC had a number of key features, the chief one was the PK, which allowed the submarine to manouver and have all the relevant target position still be updated correctly, if you changed course or speed.

Another main part it had was the SBC, the sound bearing converter. This device takes the target speed and course into account and allows sound only bearings to be converted into actual bearings. As sound takes some time to travel through water, this can cause the sound to be on a different bearing to the actual bearing of the propellers, as the bearing will lag behind. This is made worse by the propellers being at the back. The SBC took the target length and speed and course and worked out for you, based on the sound baring, what actual bearing the MOT was. This is of no use in SH4, as in SH4, sound travels instantaneously, so sound bearing are the same as optical bearing.

The mark 3 TDC operated within a target range of 400 - 8,000 yards, with the mark 4 operating between 400 and 40,000 yards. The mark 4 TDC also had an extra receiver section, which had repeaters for all the sensors, e.g. radar bearing, sonar bearing, optical bearing and range repeater from radar, stadimeter and sonar. This reduced the amount of communication necessary and therefore also reduced errors. Note that this wasn't an automatic entry, it was just a repeater display.

One feature that isn't implemented is the ability to control time in the TDC. You can wind time forward and backwards. To take an example, let's say you were trying to intercept a fast convoy and you knew you couldn't get ahead, as they were travelling faster than you, so what you could do is wind the time forward and watch the range and see at what point you would be closest to the target. E.G. in 3 hours 27 minutes we will be the closest to the target. You can also wind time back to the start and put in a different speed and then wind forward to your second onbservation and see how the two compare. Or put in a different course or whatever.

The main use though is the PK being upto date on the historical data, so that you can compare bearings and ranges with the observed ranges. Doing that you can detect zigs toward or away or changes in speed more easily than doing it on paper.

O'Kane used the TDC by having the operator wind the bearing backwards, thus holding the bearing at the same bearing as the periscope or UZO, which effectively allowed him to accurately aim at the point at which his line of sight intersected the target's course and maintain an accurate torpedo gyro angle for that point, which is something that you can't easily do with verctor analysis on the fly, unless you are on a pre-calculated and fixed course.

Er, other things the one of the versions of the Mark 3 had was a range to track indictaor, which would tell you how far you were from the target's track, which is useful if you want to avoid being too close or too far away from the target when you get in position.

[Bilge_Rat]

Originally Posted by Nisgeis

The chief crippled feature is the adjustment of the bearing, which messes up the target course, which destroys your whole solution and causes lots of frustration for new users of the TDC.

could you explain that Nisgeis, I am not sure what you are referring to.

[Nisgeis]

Originally Posted by Bilge_Rat

could you explain that Nisgeis, I am not sure what you are referring to.

OK, you know how the German TDC is linked to the periscope, so that once you have the target course layed in, if you move the 'scope then the AoB gets updated, so the solution is correct?

Well, the US TDC has a similar feature. Let's say you are tracking a target at a speed of 6 knots, on a course at 90 degrees to your own course. If you suddenly notice that the target is gong much faster than you thought and you update the bearing, then in the real TDC, the range and AoB and everything do do with it would be updated at the same time, as the PK moves the ship along its course with a bearing change. Note that the TDC is not directly linked to the periscope, because that would mess up the PK, which is the fundamental reason why it is not directly connected, but the functionality of the German TDC is there.

In the SH4 one, you have to guess or measure with the stadimeter the range again at the same time as you send the bearing (as you have to send both together D'OH!), as otherwise it will still use whatever range it had as it isn't connected, but worse than that, it will still use the AoB it already without updating it based on the bearing change, so if you advanced the bearing by 10 degrees, the AoB used would be the old one prior to your change and therefore the target's course would be changed by 10 degrees, which would make a mess of your solution.

So, what would be a simple bearing change, means you have to re-enter everything again, hardly the refinement of a solution the TDC was designed for. It also ramps up the amount of work you have to do if you discover an error at a late stage of the attack.