The Royal Marines are part of 3 Commando Brigade. The overall brigade commander is the Commandant General based at Whale Island, Portsmouth. However the Marines will be often placed under the Command of the Captain of the Ship they are attached to.
3 Commando Brigade's normal strength is 7000 men (and women) gathered from all areas of the Armed Forces.
At the core of the brigade are 3 Commando Units.
40 Commando (based in Taunton)
42 Commando (based in Plymouth)
45 Commando (based in Arbroath)
Each of these Commandos are equivilent to a Light Infantry Battalion and contain around 650 Marines.
A Commando is an independant entity and is capable of Operating by itself or with support units from various parts of the Armed forces including other specialist commando units such as
29 Commando Brigade Royal Artillery
Territorial Army Commando Battery