The two groups were taking part in a training exercise at a battleground facility in California
The Royal Marines forced US troops to surrender just days into a training exercise in California, forcing the American troops to ask for a "reset".
According to the Ministry of Defence (MoD) the battle exercise was testing the deployment of the new Littoral Response Group (LRG) in a guerrilla war-fighting facility on the west coast of America against well-equipped US Marine Corps opponents.
The exercise was the culmination of two months training in the Mojave Desert.
However the US Marine Corps had to end up asking for a "reset" just half way through the exercise as the Green Berets of the Royal Marines dominated the battle, the
Telegraph reports.
The LRG is one of two new Royal Navy task groups focused on commando forces that are able to respond to world events. One group will be based in Europe and another in Oman to focus on military threats east of the Suez Canal.
LRG South, the Oman-based group, were the ones taking part in the five-day exercise which was known as Green Dagger.
Green Dagger is attended by forces from a number of countries and is designed to test US Marine Corps units before they are deployed overseas.
In the weeks leading up to the operation, the LRG South trained with troops from the US, Canada, UAE and the Netherlands.
The commandos of the LRG proved far superior to the US marines at the Marine Corps Air Ground Combat Center in the Californian desert, a training ground roughly the size of Luxembourg.
At one point in the battle, which was focused on three urban sprawls purpose-built for military exercises, the Royal Marines' "kill board" - an intelligence assessment of the level of damage inflicted upon enemy equipment and units - had a tick against almost every American asset, indicating it had been deemed destroyed or rendered inoperable.
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."
The Royal Marines' success was achieved by targeting the US headquarters and valuable equipment, paralysing counter-attacks from the Americans.
By the end of the exercise, the Royal Marines were in control of 65 per cent of the entire area, having started with less than 20 per cent.
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