The UK is to commit warships, Typhoon fighter jets and almost 3,000 troops to the biggest Nato military exercise to take place in 13 years.
Exercise Trident Juncture will feature 36,000 service personnel from more than 30 nations, and has been organised to test how the allied group will respond to crisis situations.
Armed forces from the Navy, Army and RAF will take part in the five-week exercise which begins tomorrow in Italy, Portugal and Spain.
It is the biggest Nato exercise since 2002 and will feature the UK's two largest warships - helicopter carrier HMS Ocean as well as HMS Bulwark, which was rescuing migrants from the Mediterranean earlier this year.
Defence Secretary Michael Fallon said it was "vital" that the UK work with Nato partners in a "darker and more dangerous world".
He added: "The UK will be right there at the heart of Exercise Trident Juncture - contributing nearly 3,000 troops, our two largest warships and our Typhoon fighter jets."
The training exercise will feature 230 military units, 140 aircraft and more than 60 ships from various nations and will test the readiness of a new task force set to be launched.
The Spearhead Force, Nato's new rapid reaction task force, will become fully operational next year and will feature UK troops.
In total the UK will commit around 2,800 personnel to Trident Juncture, including an Army Brigade Headquarters and Battlegroup, three Royal Navy warships and aircraft, including Typhoon fighter jets and helicopters.