[Sailor Steve]

Hitting Backspace will pause the game. Hitting it again will unpause it at 1x.

However, if you go into Silent Hunter III/Data/Cfg/Commands.en (or whichever language you're using) you can change this:

[Cmd6]
Name=Time_compr_normal
Ctxt=1,2,6,9

To look like this:

[Cmd6]
Name=Time_compr_normal
Ctxt=1,2,6,9
Key0=0x0D,,"Enter"

And you'll drop to 1x every time you hit the Numpad Enter key.