More than 1,300 troops from the British Army's 3rd Division are taking part in the largest Exercise Warfighter for 30 years.
Soldiers from the UK, US and France have joined forces at Fort Hood and Fort Bliss, Texas, to put their combined capabilities to the test.
The 10-day exercise, which started on Monday, combines real-world armour and troops on a simulated battlefield to test their warfighting readiness and future agility.
Exercise Warfighter also allows commanders to test the headquarters' ability to plan and conduct high-intensity operations.
General Sir Mark Carleton-Smith, Chief of the General Staff, said: "Warfighting capability remains the cornerstone of deterrence and the bedrock of a world-class British Army that will be more agile, integrated and lethal."
Supported by information operations and intelligence experts working remotely in the UK, all three armies will fight alongside each other to defeat a common enemy, the Army said.
Major General Mike Elviss, General Officer Commanding 3 (UK) DIV, said "it is fundamental" to be capable of working alongside allies.
"In essence, working alongside our closest allies and leveraging our relative strengths makes us more lethal as a whole," he said.
British and French forces are integrated at divisional level into a US corps for this year's Warfighter, with US brigade combat teams inserted into each British and French division.
This year is the first time a UK Brigade, 7th Infantry Brigade, will also be integrated into a US armored division – 1st Armoured Division.
Maj Gen Elvis added that "as the US Army's principal partner" this year's exercise will see the UK further integrate "unique capabilities in cyber and space that the UK is really investing in".
"When utilised with manoeuvre forces and deep fires these make us more agile, bring more tempo to the battlefield," he said.
"This is a 21st Century force in being."
Cover image: Troops from the UK, US and France are deployed on Exercise Warfighter (Picture: British Army).