The event did take place. In October 1983, the Marine barracks at the Beirut International Airport were destroyed in a truck-bomb attack killing 241 US troops, mostly Marines. What is routinely omitted in this story is the context.
In short, the United States provided authorization and support for Israel's invasion and devastation of Lebanon. The principal goal was to destroy the PLO, which was based there in exile. The thinking went (absurdly) that if the PLO was defeated, so too would Palestinian nationalism.
At the end of Israel's "Peace for Galilee" experience, some 20,000 people were dead, the vast majority being civilians; for sake of comparison, the 1999 conflict in Kosovo claimed 10,000 lives. A brief blog post, or mere words for that matter, cannot sufficiently convey the nightmare Lebanon was reduced to in the early 1980s, all with White House consent.
American Marines were eventually sent (also absurdly) as part of a peacekeeping contingent. However, the US presence shifted to one of belligerence at the behest of President Reagan's advisers. It is critical to note that the Marine commander stationed in Lebanon strongly objected to this change in role for fear of it endangering his soldiers, and was overruled.
The US naval bombardments - on top of the murderous havoc already wreaked by Israel - inspired a group of militant locals to respond. Hence the barrack bombing.
The attack was a senseless loss of life. The Marines did not belong in Lebanon, and were put at risk the minute the White House ordered the naval assault. As for those responsible for the barrack bombing, a conversation is worth having whether it was terrorism or the act of militants attacking foreign troops - foreign troops of the country sponsoring the destruction of theirs.
Much of the practical and moral culpability - for Lebanon's losses, Palestinian losses, as well as the death of the American personnel that day - falls squarely on the mandarins of the Reagan administration. Despite Israel's involvement and those who architected the truck-bombing (and their alleged Syrian and/or Iranian backers), the following questions are raised: Who approved Israel's invasion in the first place? Who could have stopped it? Who sent in US troops? And who, after being warned of the dangers to those soldiers, called for the military to become directly involved?
More meaningful adjudication would have been bringing the president and his advisers before a war crimes tribunal, for which they were eligible, and not just for Lebanon.
