When suicide bombers strike, the shadowy men who dispatch their charges then step back to gauge the response. Thirty years ago Wednesday, after one of the costliest acts of terror ever committed against America, Washington sent out the worst possible message to terrorists around the world. They were watching and listening.

Early on Sunday morning, October 23, 1983, when our Marines were still asleep in their cots at the Beirut International Airport, a truck driven by an Iranian, Ismail Ascari, and filled with explosives crashed into their barracks. The blast was so huge that witnesses said the four-story building actually lifted into the air before it came crashing down.

The blast killed 220 Marines, more than any day since Iwo Jima — 18 sailors, three soldiers and six civilians. Almost simultaneously, a second suicide truck bomber blew up a nine story building on the other side of the airport killing 58 French paratroopers.

The Americans and French were in Beirut as part of an international peacekeeping force sent to quell the violence from the Lebanese Civil War. Once a beautiful and tranquil country, Lebanon descended into a living hell after the P.L.O. arrived, having been kicked out of Jordan by King Hussein in 1970. This tipped the fragile balance between Arab Christians and Muslims. Soon they were fighting each other as well as the Israelis, who entered in 1982 to stop PLO terror raids.

Then a new actor inserted itself into Lebanon. The Ayatollah Khomeini sent the Iranian Revolutionary Guards to train Shia militias, which would soon morph into Hezbollah, Iran’s proxy army that today controls much of Lebanon. Within three years of their revolution, the Iranians were already playing their long-term strategic game of chess.

Because Washington didn’t want the Marines to appear warlike, they were unable to defend themselves. The Marine guards posted outside the barracks on that Sunday morning were not allowed to carry live rounds in their chambers for fear of shooting a civilian.

After the bombing, a debate took place within the Reagan administration as to how to respond. The leading advocate for vigorous retaliation was the secretary of state, George Shultz. The defense secretary, Caspar Weinberger, argued against any further entanglement. Weinberger prevailed.

President Reagan, who had told the world the United States would never back down to terrorists, did exactly that when he pulled everyone out four months later.

All the Lebanese factions saw this. The Iranians saw it.  A little known Saudi, Osama bin Laden, saw it as well. Later, bin Laden would tell ABC News, the fact that “the Marines fled after two explosions” showed the “decline of the American government and the weakness of the American soldier.”   

Bill Cowan was a Marine lieutenant colonel who was sent to Beirut with a six-man team to track down those responsible. He worked closely with the CIA station chief, William Francis Buckley. Just before they left, Colonel Cowan showed Buckley what they found. They knew who did it, where they were, and how to get them.

“I remember Bill Buckley standing in the doorway holding the paper.” Says Colonel Cowan. “He said it was a good report, but it would probably be ignored.”

Then, Buckley sighed and told Colonel Cowan: “If we really want to get those responsible, we’ll need to run B-52 strikes over Damascus.” It was an allusion to the Tehran-Damascus axis.

That was intuitive on Buckley’s part. What he did not know – what almost no one knew – was that the NSA had intercepted a cable between the Iranian ambassador in Damascus and the foreign ministry in Tehran acknowledging a directive for a “spectacular action against the U.S. Marines” – one month before the bombing. The intercept was never passed on to the Marines or anyone else until after the bombing.

We will never know what might have happened had those pushing Reagan for a real response prevailed. We do know that by not responding, the following did take place:

The Khobar Tower bombing in Saudi Arabia in 1996 (19 Americans dead), the embassy bombings in Africa in 1998 (224 dead), the U.S.S. Cole in Yemen in 2000 (17 sailors dead), 9-11 (2,977 dead), and everything since.

William Buckley was abducted by Hezbollah five months later and tortured for more than a year before he finally died. His body was unrecognizable. Colonel Cowan retired form the Marine Corps in 1985, disgusted with Washington’s lack of resolve. “We had them in our sites after the barracks bombing, and we were ordered to stand down.”

In 2007, a United States district judge, Royce Lambert, ordered Iran to pay the survivors and families of the bombing $2.6 billion dollars. Iran has ignored the ruling

One of the top Iranian Revolutionary Guard commanders sent to Beirut at that time to train the Shia troops that would become Hezbollah was Hossein Dehghan. This past August, Hossein Dehghan was appointed as Iran’s new minister of defense by President Hassan Rouhani.

The Iranian Mullahs have long memories. They have never forgotten America’s role in installing the Shah in 1953. They are determined and have been extremely successful in projecting their influence throughout the Middle East and far beyond. 

Most Americans don’t know the names of any of the Marines killed 30 years ago or that the event ever happened. And they certainly don’t know who did it.

It wasn’t always this way. 

Just 4 months after Pearl Harbor, Franklin Roosevelt sent 16 B-25 bombers off an aircraft carrier to bomb Tokyo. It was close to a suicide mission, but FDR reasoned it was crucial to show Japan and the world American resolve. The bombing inflicted little damage, but it demonstrated American courage, ingenuity, and determination.

Over the past 30 years, and especially since the election of Barack Obama, the United States has projected something else altogether. And the other side is always watching … always measuring.

Mr. Kozak is the author of “LeMay: The Life and Wars of General Curtis LeMay” (Regnery 2009).