Here is what we know so far about the target and the outcome of the strike.
- The target -
At around 8:40 pm Eastern Time (0040 GMT) on Thursday, the US military fired 59 Tomahawk missiles at the Shayrat airfield near Homs in western Syria.
According to the Pentagon, the facility was used to store chemical weapons and Syrian aircraft.
The Tomahawks targeted aircraft, hardened aircraft shelters, petroleum and logistical storage, ammunition supply bunkers, air defense systems and radars, the Pentagon said.
Pentagon spokesman Navy Captain Jeff Davis said the strike lasted "a couple of minutes."
US intelligence agents believe aircraft from Shayrat conducted the chemical weapons attack on April 4.
National Security Advisor H.R. McMaster said measures had been put in place to avoid hitting sarin gas stored at the airfield.
"So that would not be ignited and cause a hazard to civilians or anyone else," McMaster said.
- How it was launched -
The strike was launched from the destroyers USS Porter and USS Ross in the eastern Mediterranean.
Russian forces were warned ahead of the strike using a special military-to-military hotline.
Signup to our newsletter and follow us on Facebook and Twitter!
Davis said the strike was designed to avoid casualties.
"Every precaution was taken to execute this strike with minimal risk to personnel at the airfield," he said.
There was no immediate indication that Russia had tried to shoot down any of the missiles.
- The result -
According to the Pentagon, initial indications showed the strike had severely damaged or destroyed Syrian aircraft, infrastructure and equipment at Shayrat.
Davis said the runways themselves were not targeted.
US officials stressed the strike was a direct reaction to the chemical attack, and not the beginning of a broader military front against Assad.
"The strike was a proportional response to Assad's heinous act," Davis said.
- Legal concerns -
The strike was launched at the order of President Donald Trump and was a "proportional response to what was a violation of international war by the Assad regime," Davis said.
But critics questioned whether the action amounted to a declaration of war and said Trump should have gone to Congress first.
America is currently hitting Islamic State targets in Syria under a 2001 Authorization for the Use of Military Force (AUMF).
But attacking the government of a sovereign nation raises legal questions.
"President waging military action against Syria without a vote of Congress? Unconstitutional," Democratic Senator Tim Kaine wrote on Twitter.