There has always been some sort of speed measuring system. Sailing ships used a rope with knots and measured how many knots were counted in a set time, which is why speed is still referred to as “knots”.
Speed measurement was more accurate in WW2, but still subject to the vagaries of weather, ocean currents, etc. which is why ships using “dead reckoning” (speed+heading) would quickly build up navigation errors and would require periodic navigational fixes. It was only once the navigator determined the exact position that the exact speed could be calculated.
Exact speeds could only be calculated on the fly once ships were equipped with INS and/or GPS systems post-WW2.
So yes, the speed measurements in SH5 and most other WW2 sub sims are too accurate, but fine for a game.
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