Let this dumb reviewer be. He is obviously unfamiliar with both the USMC and the SAS.

Delta Force was directly modeled on the SAS. Therefore, it is the U.S. equivalent. Period.

Navy SEALs are the Navy's special warfare group. They are maritime surgical strike teams. They are very comparable to the UK's Special Boat Service.

USMC and Royal Marines are also pretty comparable, though Royal Marines is a smaller service, as is everything else of Britain. Royal Marine Commando's may be considered Special Operations (I'm not sure about this), and if they are, they are somewhat comparable to USMC Force Recon. However, Force Recon is NOT a primary DIRECT ACTION force. Meaning, they're primary mission is NOT combat, it is long range reconnaissance.

Finally, about requirements in joining the SAS, it is a British Army organization, though they accept recruits from the Royal Marines. There is a prior service tenure requirement, but I am unsure of it.