A convicted child sex offender was snared by paedophile hunters when he turned up to meet an underage boy in a Sunderland supermarket car park.
Former airman Andrew Dixon was banned from having any contact with children when he struck up graphic chat over gay dating website Grindr with a supposed 15-year-old boy called "Martin" last September.
The court heard when the 52-year-old arrived at Asda in Pennywell, Sunderland, to meet the boy for sex, he was confronted by Guardians of the North.
The anonymous group set up fake profiles over social media and dating sites to snare adults looking for illegal contact with children.
Prosecutor Alec Burns told Newcastle Crown Court: "The defendant and Martin had a number of exchanges.
"What it came down to was he wanted to meet Martin for sex.
"It was obvious the person he was dealing with was claiming to be 15 years of age."
Dixon, of Patey Court, Linthorpe, Middlesbrough, who was jailed in 2007 for indecently assaulting a female child, had a hoard of 3,811 sickening images of children, as young as two or three, being abused stored on his home computer.
He pleaded guilty to attempting to meet a child following sexual grooming, breach of a sexual offences prevention order, which was imposed after his last sentence, and possessing indecent images.
Judge Stephen Earl sentenced him to 33 months behind bars with a lifelong Sexual Harm Prevention Order and sex offender registration.
The judge told him: "Those messages make it exceedingly clear Martin was a schoolboy of 15. The messages make that abundantly clear to anyone capable of reading them."
Jamie Adams, defending, said Dixon was discharged from his 22-year post of electrical engineer in the air force when he was convicted and jailed in 2007
Mr Adams added: "He is intellectual, he is articulate and can express himself.
"There has to be something wrong with him for him to be coming before the court again in this kind of way.
"He, thankfully, himself readily accepts that."
Mr Adams said Dixon had found new work after his release from the 12-month 2007 prison sentence and has recently volunteered as a mentor and listener in custody.
He added: "He is doing all he can to try and put things right."