Royal Marines have defeated the US Marine Corps while testing a new formation during a fiery five-day exercise battle in California's Mojave Desert.
The British marines joined forces with troops from four other nations to test the newly-formed Littoral Response Group (South) (LRG(S)) against the 'highly-equipped' adversary.
The exercise at the vast US Marine Corps' training facility at Twentynine Palms focused around three urban sprawls which were defended by the allied forces, the largest of which consisted of 1,200 purpose-built buildings.
The gruelling battle was the culmination of exercises, known as Green Dagger.
Royal Marines have spent the last two months in the Mojave Desert preparing for deployments next year as part of the LRG (Littoral Response Group).
It is one of two new Royal Navy task groups centred on commando forces set up to respond to world events – a continuation of transforming how the UK Commando Force operates.
Watch: Forces News joined HMS Albion on last year's Littoral Response Group (Experimentation) (LRG(X)) deployment off Cyprus.
Experts from across 3 Commando Brigade came together to form the LRG – with Taunton-based 40 Commando at its heart.
Personnel from the US, Canada, United Arab Emirates and the Netherlands joined forces with the Royal Marines to make up the formation.
The LRG won decisive battles "early on" into the battle exercise, the Royal Navy said, gaining ground on its enemy.
As US Marines pushed into the allied territory, the Royal Marines and their allies carried out raids behind enemy lines to stop further counterattacks.
Lieutenant Colonel Andy Dow, Commanding Officer of 40 Commando, said the success of the exercise has "proved the new commando force concept is more lethal and sophisticated than ever before".
"I am immensely proud of every member of the LRG and their vital contributions," he said.
"Operating alongside our partners from the USA, Netherlands, Canada and the UAE gives us a fantastic opportunity to test, integrate and continue to push our capabilities in new and innovative directions.
"Throughout this deployment our focus has been on integrating game-changing capabilities from across the commando force to deliver disproportional effect in the face of a free-thinking peer adversary."
The exercise concluded with a last-minute 'enemy' assault which was repelled, leaving allied forces in control of more than two-thirds of the entire battlefield.
The deployment has ultimately readied the commando element of LRG(S) for operations next year, joining its sister task group, Littoral Response Group (North).
The LRG (North) has already deployed to the Baltic this year and has a focus on events across Europe, while LRG (South) will operate east of the Suez Canal.
LRG (South) is expected to be functional next year with the addition of amphibious ships and aircraft.