Ian Naude, 30, of Market Drayton in Shropshire, was working as a constable in Cheshire Police at the same time as operating as a "prolific internet groomer", his trial at Liverpool Crown Court heard.
Owen Edwards, prosecuting, said Naude had been called to a domestic incident in October 2017 when he took down the details of a 13-year-old girl who lived at the address.
Three days later he returned and picked the girl up before taking her to a quiet spot in his car where he allegedly raped and sexually assaulted her, recording some of the incident on his mobile phone, the jury was told.
The court heard Naude had admitted sexual intercourse and sexual activity with a child but claimed it was consensual.
Mr Edwards said: "She had been groomed by a police officer who was experienced in the art of manipulating, pressurising and even blackmailing young girls into performing sexual acts for his perverted pleasure."
The court heard a police investigation, started after the teenager reported the alleged assault to her family, discovered it was the "tip of the iceberg" of Naude's alleged offending.
"Naude is a committed paedophile who had been targeting young girls on the internet for a considerable period," Mr Edwards said.
"Shockingly it emerged that he had joined the police with the intention of exploiting the access he would gain to vulnerable young girls.
"In essence, he was hoping to gain the keys to a sweet shop."
He said Naude was "obsessed" with taking the virginity of teenage girls and would make them call him "daddy".
The Pc, who has admitted a number of child sex offences, would gain the trust of young girls by posing as a 15-year-old boy called Jake Green, the court heard.
He would persuade his victims to undress and sometimes perform sexual acts on camera before sending them pictures and video of himself masturbating, the jury was told.
As well as denying rape and sexual assault, Naude denies four charges of attempting to arrange the commission of a child sex offence and one charge of arranging a child sex offence, relating to five complainants aged between 12 and 15.
Mr Edwards told the jury: "His defence is that there were limits to his depravity, you will have to decide where the truth lies."
As well as admitting sexual activity with a child, Naude has pleaded guilty to two counts of engaging in sexual communication with a child, 14 counts of inciting a child to engage in sexual activity, one count of taking indecent photos of a child, four counts of making indecent photos of a child, six counts of causing a child to watch a sexual act, two counts of misconduct in a public office and one count of possessing indecent photos of a child.
The trial is expected to last around three weeks.