The Long Commission Report was very closely held, at the time only five people including John Guenther and Robert Steele, had access to the entire report. Here’s the bottom line:
1) The threat changed and no one noticed. The battalion commander, who had previously served as the senior Marine in the CIA’s Special Operations Group (SOG), was told he was in a benign threat environment in which casual shrapnel was the highest threat to his troops, and it therefore made sense, if they were to be billeted ashore (Navy cannot stand dust and bootmarks on its lily decks), to put them in a solid building.
2) Policy-makers had no clue about the connection between their behavior and the threat. They thought lobbing in battleship shells the size of small cars would “send a message” without realizing that a) this changed the Marine Corps role from peace-keeper to belligerent; and b) they might inspire a message back.
3) National intelligence then–and now in Afghanistan–was completely useless. The national intelligence community is not trained, equipped, nor organized to do tactical intelligence, and after Marty Hurwitz got done destroying tactical intelligence in favor of theater intelligence centers far removed from the battlefield, neither tactical nor joint operational capabilities were at all adequate.
4) The Rules of Engagement (ROE) were designed by flag officers more concerned about mis-fires than actually protecting our force. Every flag officer passing through validated the battalion commander’s use of the building, and failed to recognize the idiocy of hand-cuffing Marines from defending their own barracks.
USMC 22nd MAU Beirut Lebanon 1983 1984 (9 Minute Video with Slide Show)