Graham Jarvis, 38, struck a deal with a woman he met online to sexually abuse her children, and planned to travel from his central London barracks to her home in Wales to commit the offences.
However he was actually chatting with an undercover police officer posing as the mother.
At Southwark Crown Court on Thursday, Jarvis was sentenced to 12 years in prison for two counts of attempting to arrange the commission of a child sex offence.
Jarvis, who was living at barracks in Hyde Park, denied the offences and was convicted at a trial.
He has been ordered to serve at least two-thirds of his 12-year prison term.
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