The mission to target so-called Islamic State militants in Syria could take some time and will require persistence, PM David Cameron has said.
RAF Tornados conducted air strikes on six targets in Syria, "successfully" attacking an IS-controlled oilfield, the Ministry of Defence confirmed.
There will be "strong support from our allies" for the action, the PM added.
It comes as two additional Tornados and six Typhoons have arrived in the region from the UK to take part in attacks.
Speaking after the strikes, Mr Cameron said the operation in Syria would require "patience".
"It is complex and it is difficult what we are asking our pilots to do, and our thoughts should be with them and their families as they commence this important work," he said.
The decision to approve the mission was "good for the country", the prime minister said, adding: "There was a compelling case for extending our air strikes from Iraq to Syria, and I was glad to see such strong support right across parliament."
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