http://www.addictinginfo.org/2013/05/09/why-were-republicans-silent-when-reagans-benghazi-killed-241-american-servicemen/

Those Marines had been ordered into Lebanon by President Ronald Reagan as a part of an international peacekeeping force following the June 1982 Israeli invasion of that country and the Palestine Liberation Organization’s withdrawal.

Making an already-dangerous situation even more hazardous, the Marines were under strict presidential orders not to load their weapons — this, so that they would appear as peacekeepers and not as armed belligerents in the conflict and despite the fact that they were moving into a war zone.

Realistically, they had become “sitting ducks” from the moment they entered Beirut. And as a result of their absurd orders, when the explosives-laden truck sped toward their doomed barracks, the two unarmed guards had no way of stopping it.