Royal Marines Commandos
(right) pictured on a room clearing exercise with US Marines in the U.S., 2007. Note the M4a1 Carbines carried by both the UK and US Marines. The 5.56mm x 45mm caliber M4 is the standard carbine of the US military and is similar to the C8 SFW carbines
used by some elite UK units.
U.S. Marine Corps photo by Pfc. Shawn M. Statz/Released