Jamming of GPS in parts of Scotland is likely during Europe's largest military exercise next month, the Ministry of Defence (MoD) has said.
Jamming during Joint Warrior last October was suspended after complaints from Western Isles fishermen.
The islands council, Comhairle nan Eilean Siar, also said satellite TV, mobile phones and internet connectivity were disrupted.
The MoD said prior warning would be given of any jamming.
Joint Warrior will run from 16-26 April.
The war games and counter terrorism training are held twice a year, in spring and autumn, and involve Nato armies, navies and air forces.
Much of the training takes place in Scotland.
The Royal Navy has already alerted fishermen to the possibility they will be challenged by helicopters and ships in radio communications as part of the training.
Timings of any disruption to civilian users of GPS has still to be confirmed.
Jamming was done during previous exercises, but was suspended last year after the complaints were made.
The Royal Navy had issued prior warnings that GPS in parts of Scotland would be disrupted, including in a guide made available to the public the previous month.
It gave the locations and timings for the jamming.
The Scottish government also confirmed it had received the guide and put it on its website.
However, Western Isles fishermen said the first they knew of the jamming was when their equipment went offline.
Comhairle nan Eilean Siar said jamming had also been blamed for affecting internet connectivity and mobile phone and satellite TV.
The MoD has issued a notice to fishermen setting out some of the activities in, or near, areas where they work.
According to the Royal Navy, the notice has been distributed to coastguard stations, Scottish Fisheries Protection Agency offices and fishing organisations, including the Scottish Fishermen's Federation and Western Isles Fishermen's Federation.
Durness Community Council and Aultbea Post Office in the north west Highlands have also been sent the details.
Joint Warrior will see minehunting involving the Royal Navy, Norwegian and German vessels in and around the Minch, Loch Ewe and Loch Eriboll.
The British minehunters will include HMS Brocklesby which took part in operations against Col Muammar Gaddafi's forces in Libya last year.