HMS Ark Royal will be among 21 warships on the exercise
Army, navies and air forces from Nato countries have gathered in the UK for the start of Joint Warrior - Europe's largest military exercise.
UK-led and running until 23 April, it will see training in Scotland and in the sea off its coast.
Aircraft will be flying from RAF stations at Kinloss and Lossiemouth in Moray.
Training will also take place at Cape Wrath in Sutherland and around the Western Isles.
The exercise will involve 16 Air Assault Brigade and the Royal Navy's Carrier Strike Group headed by HMS Ark Royal.
Soldiers, sailors and air crews from 12 other countries, including the US, will also take part.
Twenty-one surface ships, five submarines and 50 aircraft will be deployed around Scotland and the rest of the UK during Joint Warrior.
The exercise is held twice a year - in spring and autumn.
Last year's second Joint Warrior saw two gunners escape with minor injuries after their vehicle toppled off a bridge and fell 30ft into a river.
The members of 29 Commando, Royal Artillery, were travelling in a Drops transporter to Cape Wrath.
Their vehicle came off the A838 Lairg-Durness Road at Laxford Bridge.
The Army said the pair had cuts and bruises. The transporter was carrying a digger.
Major structural damage was caused to the bridge and it had to be closed for repairs.