Well i f u dont have the ime for books u can use 1 simply rule:
ALL US ships use 110V/60Hz electric curent....The rest of the ships NOP!
So they (US) need 60Hz generator...and 60 is wery low frequency wivh means it can propagate quite far away from ship...If u chasing US sub just put alerter to 60..If u chasing Russians put it ot 50 and watch the show!