Ali Kalama believed he had been chatting to a 14-year-old virgin over the internet but had been duped by pervert hunters Guardians of the North.
Newcastle Crown Court heard the organisation, which aims to expose adults looking for illegal contact with children, had set up a fake persona of a girl called "Louise".
The 33-year-old dad, who previously served in the Royal Logistics Corps, was warned he was speaking to someone underage but "within three messages" had turned the conversation to sex.
Prosecutor Mark Guiliani told the court: "Within three messages of this being said, the defendant then said 'have you had sex before' and she said she had not had sex before.
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He added that Kalama then sent her an indecent image.
The court heard despite "Louise" talking about still being at school, Kalama arranged to meet the girl at Park Lane Interchange, in Sunderland, on May 15 last year.
He was confronted by Guardians of the North when he arrived and then arrested.
Kalama, of Campbell Street, Peterlee, initially claimed he thought he had been chatting to a woman on the adult site and that the talk about being 14 was just "fantasy".
He later admitted attempting to met a child after sexual grooming.
Judge Stephen Earl sentenced Kalama to 14 months' imprisonment, suspended for two years, with rehabilitation and sex offender programme requirements with and sexual harm prevention order.
He must also register as a sex offender for a decade.
The judge told him: "You turned up intending that Louise be there and intended there be some sexual contact between you, it can only have been your intention
at that time."
Judge Earl said the suspension of the prison term meant Kalama's "beliefs and behaviour" can be addressed by professionals.
Tony Cornberg, defending, said Kalama arrived in the UK from Kenya in 2007 after he met his wife while she was on holiday in his country.
He joined the army as a driver in 2010 but was medically discharged last year after working in Germany, Kenya, Canada and Afghanistan.
Mr Cornberg said Kalama was "lonely" and was living in a new area after his marriage split when he committed the offences.
Kalama told the court "I'm really sorry I have done wrong".