After an impassioned 10-hour Commons debate, MPs have overwhelmingly backed the UK air strikes against so-called Islamic State in Syria, by 397 votes to 223.
A total of 66 Labour MPs sided with the government as David Cameron secured a larger than expected Commons majority. The PM said they had "taken the right decision to keep the country safe" but opponents said the move was a mistake.
Four Tornado jets took off from RAF Akrotiri, Cyprus, after the vote. Their destination has not been confirmed. A further four fighter jets remain on standby at the air base, which is used for bombing missions to Iraq and from where reports have suggested air strikes against IS targets in Syria could also be launched.
Two of the four Tornados landed back in Cyprus just over three hours later, shortly before 03:00 GMT.The BBC reports that they had left RAF Akrotiri with three 500lb Paveway bombs each and returned to base without those weapons.
The Ministry of Defence is expected to give details of their targets later on Thursday, he added.
BBC political correspondent Robin Brant said while the Ministry of Defence was not confirming where the jets were heading, it "would not be surprising" if they were bound for Syria.
Foreign Secretary Philip Hammond said he would not give a "running commentary" on operations, having earlier suggested bombings could begin as early as Thursday. Welcoming the Commons result, Mr Hammond said Britain was "safer because of the actions taken by MPs today".
He added: "Military strikes alone won't help Syria, won't keep us safe from Daesh. But this multi-strand approach will."
Labour leader Jeremy Corbyn, argued that the case for war "does not stack up" - but his party was split, with senior Labour figures, including members of the shadow cabinet voting with the government after they were given a free vote. The 66 MPs who backed military action was equivalent to 29% of the parliamentary party.
Shadow foreign secretary Hilary Benn was applauded by MPs from across the House, particularly on the Conservative benches, when he urged his own side to "confront this evil" posed by Islamic State, who he said "held our democracy in contempt".
In an impassioned speech, Mr Benn said the international community was "faced by fascists and what we know about fascists is that they must be defeated". While there were "rarely perfect circumstances to deploy military forces", he said "the threat is now" and the UK must rise to the challenge.