2,500ft would make a Lynx a very nice target for a ship launched SAM, hence the need to fly so low whilst searching for contacts.
Also the Flight LAC is responsible for keeping tabs on the endurance of the aircraft, the ships position from outhouse, and if possible, the position of the aircraft. Thus leaving the Navigator to avoid ships, reefs and large islands (or not)!!
Totalwar, OUTHOUSE is antiquated, but as long as mum remains within 10nm of it, there is no reason for it all to go wrong. In these days of GPS, the old "plot slippage" problem 42's used to suffer has been sorted. Also the 20 minute aviation cycle helps safeguard against OUTHOUSE wandering off unnoticed. Maybe in the future, with more and more data link fitted helicopters being used, a more reliable procedure could be used.