Speed and depth tolerances, please
 

I'm working through the training missions and find that the Porpoise will not exceed about 7 kts submerged. I'd appreciate knowing if this is to be expected and if so whether submarines of this era (I'm coming from SC/688i) had to cruise on the surface in order to pursue distant targets. It would be helpful also to get some maximum submersion parameters. The manual supplies none of this information.

Thanks.

7 knots or so is about as good as you'll get, and even then you'll deplete the battery quickly running flat out. WWII subs are surface vessels that submerge, not submarines in the modern sense.