Ships, land forces and aircraft and more than 11,000 personnel will take part in a virtual battle around the UK on Exercise Joint Warrior.
The huge exercise begins on Saturday 1 October, led by the Royal Navy, in which NATO forces will be tested from Cape Wrath and the Hebrides to the North Sea and Channel.
More than 20 ships and some submarines, including Royal Navy destroyer HMS Diamond and frigates HMS Kent, HMS Northumberland and HMS Somerset, as well as a couple of Royal Fleet Auxiliary tankers, are taking part.
They are joined by vessels from the US, Poland, Denmark, Norway, Germany, Netherlands, Canada, France and Latvia, the Navy said.
In the air, RAF Typhoon jets, long-range maritime patrol aircraft and drone technology will be involved, while planners use virtual and live aerial assets to test their responses.
Live submarines will be hunted down by anti-submarine ships, aircraft and helicopters, while 29 Commando Regiment Royal Artillery and US Marine Corps will make up land forces tasked with dealing with the enemy.
The exercise, which is due to end on 12 October, will be directed from RAF St Mawgan, near Newquay in Cornwall.
Commanding Officer of HMS Kent, Commander Jez Brettell said: "Exercise Joint Warrior is a fantastic opportunity to fully demonstrate HMS Kent's wide-ranging capabilities in close consort with other Royal Navy units, ground units, air assets and multinational forces."
"Having recently proven ourselves at Operational Sea Training, the exercise is ideally timed to consolidate our training at the very start of our deployment so that we are ready for anything that may follow."