Rubic,
I don't think anyone - even the Torygraph - has ever implied that the Royal Marines ever belonged to the Army. However, the Commandos were very much army at the beginning; indeed, the (later) Royal Marines version came in for a lot of stick as they took non-volunteers.
Love the banter, by the way - gives us something to chat about and wind up the policemen when we do our shift changes (there is life after service heli flying, you know...)