Reply #2

The earliest known use of the term "space marine" was by Bob Olsen in his short story "Captain Brink of the Space Marines" (Amazing Stories, Volume 7, Number 8, November 1932), a light-hearted work whose title is a play on the song "Captain Jinks of the Horse Marines", and in which the protagonists were marines of the "Earth Republic Space Navy" on mission to rescue celebrity twins from aliens on Titan. Olsen published a novella sequel four years later, "The Space Marines and the Slavers" (Amazing Stories, Volume 10, Number 13, December 1936), featuring the same characters using a spaceship with active camouflage to free hostages from Martian space pirates on Ganymede.
A more widely known early example was E. E. Smith's Lensman series. While the first story, Triplanetary and most later sequels (Second Stage Lensmen, Children of the Lens and The Vortex Blaster) do not mention them, passing mentions of marines are made in Galactic Patrol (Astounding Stories, September 1937–February 1938) and Gray Lensman (Astounding Stories, October 1939–January 1940), and a more direct mention is made in First Lensman (1950): "Dronvire of Rigel Four in the lead, closely followed by Costigan, Northrop, Kinnison the Younger, and a platoon of armed and armored Space Marines!".
The phrase "space marines" appears in Robert A. Heinlein's "Misfit" (1939) and is again used in "The Long Watch" (1941) which is referenced in his later novel Space Cadet (1948), in all cases before Smith had used the phrase. Heinlein's Starship Troopers (1959) is considered the defining work for the concept, although it does not use the term "space Marine." The actors playing the Colonial Marines in Aliens (1986) were required to read Starship Troopers as part of their training prior to filming. Heinlein intended for the capsule troopers of the Mobile Infantry to be an amalgam of the shipborne aspect of the US Marine Corps relocated to space and coupled with the battlefield delivery and mission profile of US Army paratroopers.
http://en.wikipedia.org/wiki/Space_marines