Marines are what Navy personell keep on board their ships for entertainment on those long voyages........no not really, Marines are more of an amphibious mobile unit, that canusually do more with less than what it takes the army to do. The army is strictly land based operations where marines assault from land or sea, and are pretty capable of doing most operations with fewer men and older equipment in out of the way locations. (Not talking any special forces types such as Green Berets, Rangers, Seals etc etc, just out and out reg military type troops. If you notice the marines seem to get older equipment as comparaed to the Army (They fly cobras, army has latest and greatest Apache). The marines are more self supporting as well, as they have their own air wings both fixed and rotary, so its their own guys that do the close air support and know the ropes of the game. The army relies on the NAVY, USAF and MArines to support them for CAS stuff, in addition to their Apache helios etc.
Marines still use the old M-60 battle tank, which was phased ut of th US Army.....
The M-60 and the Cobras they use have been updated but its still not like having the latest and greatest like the USAF and ARMY have, but they can make it work and usually make it work great.
I have seen Marine aircraft being used in day to day operations that the USAF would have grounded. I think the USAF is more by the book 110% whereas the MArines know what can and can't be done with a peice of equipment and still can do what it takes using stuff the USAF would have grounded and do it without putting the air crews in danger......Marines are just folks that can do it all........Army relies on the USAF for support and transportation. Marines usually use Navy for transport. Marines are more or less the grunts of the Navy, trained more for water borne operations and small skirmishes that need to be handled quickly and discretely and on short notice. Marines are usually assigned to a Fleet, and there are always a contingent of marines on most ships just incase.
I have always admired the way Marines function, even though I used to be regular Army and also USAF......the marines get my vote all the time. They even have the best looking uniform(s). The Army is pretty good on uniforms, as is the Navy, but the USAF, well, all I can say there is that a USAF type can remove his stripes and ribbons and go to his second job as a bus driver.