making turns for 15 knots

vincent p. norris wrote:
The secret squirrel part is how do you find out the blade rate to
knots correlation of everyone else's submarines.


Well, ATC can give a pilot a groundspeed readout based on tracking his
progress on the radar screen. Can't something of that sort be done
with subs?

As in time-distance using two or more fixes, yes. I think the old
fashioned way was with a piece of paper, but it is nothing for a
primitive (by today's standards) computer to do it for you with two
or several fixes.

Or could the Doppler effect be used for that purpose?

Also yes, but of course if the target is not heading directly (or
near directly) towards or away from your receiver, then doppler shift
will be less pronounced. You can sanity check the "big picture"
using, among other things, doppler, fixes, and common sense.

Last, a lot of the time you only have some of the above information,
the fixes may have questionable accuracy, so then you get an
approximate solution.