Incorrect.
http://www.usatoday.com/news/military/2008-10-15-beirut-barracks_n.htm
—snip—
As interpreted by the Marine commanders, the mission precluded fortifications at their compound at Beirut International Airport that might suggest the Marines weren’t peacekeepers — such as a perimeter fence that would stop anything bigger than a car.
Similarly, sentries directly facing the airport were ***ordered to carry their ammunition on their belts — not in their rifles — to avoid an accidental shooting.****
Adding to its vulnerability, the compound was surrounded by high ground occupied by Muslim militia artillery. So to Marines leery of gunfire, the compound’s sturdy, four-story cinderblock building seemed like a haven.
It turned out to be a tomb.
—snip—