Twelve NATO nations are taking part in Exercise Joint Warrior (Picture: MOD).
The largest military exercise in Europe has got underway across Scotland and northern England.
Personnel, aircraft, ships and submarines from 12 NATO nations are taking part in Exercise Joint Warrior over the next two weeks.
Military personnel from Japan and the United Arab Emirates are also involved.
The Royal Navy, Army and RAF are all taking part - working alongside allies to conduct joint operations against a range of threats, the Ministry of Defence (MOD) said.
In total, 58 aircraft, 16 ships, three submarines and nearly 4,000 troops are taking part.
The exercise aims to test the defensive capabilities of the UK and its allies, according to the MOD.
"As we look ahead to the December NATO Leaders’ meeting in London to mark the Alliance’s 70th anniversary, Exercise Joint Warrior provides a timely demonstration of why it is the bedrock of our defence," said the Minister for the Armed Forces, Mark Lancaster.
"A wide spectrum of allies and friends will come together, build understanding and sharpen our collective defence."
The exercise is the first of five in which the Anglo-French military force, the Combined Joint Expeditionary Force (CJEF), will be able to test itself.
The UK and France have been developing the CJEF since 2010 and is hoped to be fully operational by next summer.
It is designed to take on any future crisis that is of common concern to France and the UK.
The CJEF is complementary to NATO and as part of the wider exercise, the Force will conduct a maritime exercise, Exercise Griffin Strike.
Exercise Joint Warrior is a biannual exercise run by the United Kingdom and, according to the MOD, makes up part of the NATO exercise programme.
Germany, Canada, Denmark, Norway and the United States are just some of the NATO members taking part.