Four Royal Air Force (RAF) Tornados took off from a British air base in Akrotiri, Cyprus, shortly after the 397-223 vote by lawmakers in the House of Commons.
A Ministry of Defence spokesperson said the planes had conducted strikes in Syria, and details about their targets would be provided later in the day.
The RAF has been launching strikes against IS targets in Iraq since 2014. The decision to expand the campaign to Syria came after an emotional ten-and-a-half hour debate in which Prime Minister David Cameron said that Britain must strike the militants in their heartland and not “sit back and wait for them to attack us.”
Opponents argued that Britain’s entry into Syria’s crowded airspace would make little difference, and said Cameron’s military plan was based on wishful thinking that overlooked the messy reality of the Syrian civil war.
Cameron has long wanted to target IS in Syria, but had been unsure of getting majority support in the House of Commons until now. He suffered an embarrassing defeat in 2013 when lawmakers rejected a motion backing attacks on the forces of Syrian President Bashar Assad.
The mood has changed following the November 13 Paris attacks, claimed by IS, that killed 130 people. Both France and the US have urged Britain to join their air campaign in Syria, and Cameron said Britain should not let its allies down.
‘Do we work with our allies?’
He said Britain was already a top target for IS attacks, and air strikes would reduce the group’s ability to plan more Paris-style carnage.
“Do we work with our allies to degrade and destroy this threat and do we go after these terrorists in their heartlands, from where they are plotting to kill British people?” he said. “Or do we sit back and wait for them to attack us?”
He said that attacking IS was not anti-Muslim but “a defence of Islam” against “women-raping, Muslim-murdering, medieval monsters.”
Cameron was backed by most members of his governing Conservative Party — which holds 330 of the 650 Commons seats — as well as members of the smaller Liberal Democrat party and others.
Labour, the main opposition, was divided. Labour leader Jeremy Corbyn — who represents the left wing of the party — spoke against what he called a “reckless and half-baked intervention.” But more than 60 Labour lawmakers, including senior party figures, voted in support of air strikes, a move likely to make fissures between the right and the left of the party even worse.
Labour foreign affairs spokesperson Hilary Benn said Britain could not “walk by on the other side of the road” when international allies were asking for help against IS “fascists.”
Britain already conducts air strikes against IS targets in Iraq, and in August launched a drone strike that killed two British IS militants in Syria.
British officials say RAF Typhoon and Tornado fighter jets, armed with Brimstone missiles capable of hitting moving targets, would bring the campaign highly accurate fire-power and help minimize civilian casualties.
Obama welcomes UK decision
President Barack Obama welcomed the British vote to join the air campaign in Syria, saying the IS “is a global threat that must be defeated by a global response.”
Critics claim British air strikes will make little practical difference, and that ground forces will be needed to root out IS. Britain has ruled out sending troops, and critics of the government have responded with skepticism to Cameron’s claim that there are 70,000 moderate Syrian rebels on the ground.
Cameron stood by that claim Wednesday, though he conceded, “I’m not saying that the 70,000 are our ideal partners.”
Karin von Hippel, who was chief of staff to US General John Allen when he was the United States’ anti-IS envoy, said force alone would not defeat the militants — but neither would diplomacy by itself.
“The Brits have expertise and capabilities,” she said. Their involvement “brings moral authority and legitimacy to the fight.”
The British vote came as US Secretary of State John Kerry said Nato members were ready to step up military efforts against the IS — and held out hope of improved cooperation between the West and Russia to end Syria’s four-year civil war.
A day after US Defence Secretary Ash Carter said the United States would deploy a new special operations force to Iraq to step up the fight against the militants, Kerry said other countries could provide assistance that did not involve combat. He said the effort to expand operations would require more medical facilities, intelligence-gathering, military support structure, refueling operations, aerial defenses and other action.
The German Cabinet has approved plans to commit up to 1,200 soldiers to support the anti-IS coalition in Syria, though not in a combat role.
Despite talk of increased international cooperation, tension has soared between Russia and Turkey after the shooting down of a Russian military jet by Turkish forces last week.