Well, apparently Games Workshop think they have trademarked "space marines" and nobody else is allowed to use them in works of fiction.
http://mcahogarth.org/?p=10593 Ooh, is that a copy of Heinlein's Space Cadet see nearby, published in 1948. Let's copy a couple of sentences:
"Matt killed time by watching the space marines and chinning with the non-coms.
He liked the spit-and-polish style with which the space marines did things, the strutting self confidence self-confidence with which they handled themselves."
Naughty Mr. Heinlein! Infringing on Games Workshop's trademark like that, 40 years before they released Warhammer 40k. I hope GW have a time machine handy so they can go back in time and sue him.
It's a good job GW don't derive their games from other written works, like publishing a wargame with elves, dwarves, orcs and ... no, wait.