If you use the very close approximation that 1 nm is 2000 yards, its fairly easy to do in your head. 4500 yards for example would be 2.25 nm.
It's probably not realistic but I find having to do some simple math in my head quickly while playing adds to the stress level, which makes it more fun.
Also, if you use the nomograph (see Trigger Maru for example), there is a line on the map that has nautical miles on one side and yards on the other, which gives you a visual reference to convert between the two.
EDIT: Just re-read simonpe's post. I'm not aware of any situation where ranges are directly given in feet (it's usually yards). The one exception would be the active sonar. Note that the numbers around the outside of the active sonar dial are actually yards. However, if you are tracking a target more than 5000 yards away, you can multiply the number of seconds it takes to hear the reflected sound impulse by .333 to get the distance in nautical miles away. That's 4000 feet per second dived by 3 to get the number of yards divided by 2 to account for the fact that the sound makes a round trip divided by 2000 yards per nautical mile. You can track target by active sonar this way that are 10 nm away.
Taking 1/3 of the number of seconds is easy to do in your head as well.
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