The British commandos “dominated” US forces while trialling a new battle structure in California. They eliminated almost the entire unit of US troops during the five-day fighting exercise.
US forces asked for a “reset” halfway through due to heavy simulated casualties, the Telegraph reported.
And at one point the commandos had destroyed or rendered inoperable every American asset.
Lieutenant Colonel Andy Dow, commander of the British force, said: “Throughout this deployment our focus has been on integrating game-changing capabilities from across the commando force to deliver disproportionate effect in the face of a free-thinking peer adversary.”
Exercise Dagger Green is attended by military forces from a number of countries.
The exercise is used to test US Marine Corps units before they are deployed overseas.
The area used for the exercise is over 3500 square kilometres of mountainous and desert terrain.
There are also urban settings with actors, who do not have to follow a script, playing civilians.
The British troops used the training exercise to trial the new Littoral Response Group (LRG) structure.
Following reforms directed by the First Sea Lord, Admiral Sir Tony Radakin, the UK will have two LRGs each based around an existing unit of Royal Marines.
The Royal Marines are an amphibious force of the Royal Navy.
The elite fighting force is held at high readiness for worldwide rapid response and is able to deal with a wide range of threats.