May said while the strike was targeted at Syria, it sent a message to anyone who used chemical weapons.
Mattis noted that a year ago, USA forces conducted a "unilateral strike on a single site", whereas he said these strikes "will result in a long term degradation to the Syrians' capability to research, develop, and employ biological and chemical weapons".
"This is the first time as prime minister that I have had to take the decision to commit our armed forces in combat -- and it is not a decision I have taken lightly".
In a statement Friday night, U.S. President Donald Trump outlined strikes being carried out against the Syrian regime of Bashar al-Assad after a chemical weapon attack earlier in the week.
The Organisation for the Prohibition of Chemical Weapons (OPCW) released a statement Saturday saying the organization is in Syria to conduct an investigation into the allegation that the April 7 attack in Duma was a chemical one and will remain there until the task is complete.
Jeremy Corbyn, leader of the main opposition Labour Party, has questioned the legal basis for Britain's involvement.
"America does not seek an indefinite presence in Syria", he said, thanking the United Kingdom and France for joining the USA in its fight against the Syrian regime.
Mr Corbyn said that if Britain wants to "get the moral high ground around the world" it must abide by global law for taking military action.
British lawmakers voted down taking military action against Damascus in 2013, in what was widely viewed as an assertion of parliamentary sovereignty on the use of force.
But May said intelligence pointed to the Syrian government being behind the suspected chemical attack on the rebel-held Damascus suburb of Douma last Saturday, and Defence Secretary Gavin Williamson said speed was "essential". He warned that intervention would lead to a proxy war with Russian Federation which would be "not only risky to Britain, but the entire world".
"We should not be surprised if we detect major intrusions into U.S., United Kingdom and French cyberspace and social media", Barrons said.
Professor Iain Begg, Research Fellow at the European Institute and Co-Director of the Dahrendorf Forum at the London School of Economics and Political Science (LSE), told Xinhua: "A volley of bombs may help the US and its allies feel they have reacted in a timely and proportionate manner to the undoubted horror of the use by the Syrian regime of chemical weapons, but the inevitable worry will be that they have not thought through what happens next".