the following was explaned to me by a CWO3 in iraq back in 05.
a DOD directive comes down to all four branches to secure a particular building. here is what happens............
A Sailor walks up to the building, and locks all doors and windows. Bldg secured.
A team of Airmen negotiate a contract for the use of the building, utilities and furnishings for the next year. Bldg secured.
A Soldier finds himself as part of a team forming a perimeter around the building, observing and reporting to higher headquarters. Bldg secured.
The Marine...............
the Marine is part of a rifle company assaulting the building with air and fires support.
Building Secured.