Durham Police carried out a huge investigation involving 1,800 witnesses into what happened at Medomsley Detention Centre near Consett, from its opening in the 1960s to its closure in 1988.
Christopher Onslow, 73, was convicted of misconduct in a public office as well as individual acts of violence against youths and was jailed for eight-and-a-half years at Teesside Crown Court.
He smacked one inmate around the head with muddy football boots which the teenager had not cleaned properly, leaving lasting scars, and caused another to fall from a cargo net and break his back by throwing rocks at the terrified, overweight boy when he got stuck.
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John McGee, 75, was jailed for two years and 10 months following his conviction for misconduct in a public office and assault.
Standing more than 6ft-tall, he punched a new, 5ft inmate in the face, who then soiled himself in fear, and McGee forced him to bunny-hop down a corridor to clean himself up.
Kevin Blakely, 67, was convicted after a trial of two counts of misconduct in a public office and was jailed for two years and nine months.
Judge Howard Crowson said pushing, shoving and even giving inmates a clip round the ear would not have constituted misconduct in the 1970s and 1980s.
But he said young offenders were regularly punched and stamped on as part of a regime of fear at Medomsley.
Two other officers, who were also convicted following a series of three trials, will be sentenced later this month.
The judge praised the victims' bravery and the police for taking on the massive case, decades after the violent officers would have thought they had got away with their abuse.
He said: "For many years trainees from Medomlsey Detention Centre shared a common sense of grievance.
"Many had experienced brutality and violence at the hands of prison officers, but nobody wanted to hear about it.
"Those who had the courage to complain when they were released were either ignored or warned that to pursue the complaint would risk a return to Medomsley - nobody wanted to risk that."
Judge Crowson said the country felt it easier to believe such institutions were places of appropriate discipline "where unruly boys were taught to behave properly".
He said: "In those days any complaint was likely to be regarded as further evidence that the trainee was anti-social, that he had not learned his lesson and was complaining about appropriate treatment."
He said the defendants, now elderly men, had been protected for 40 years by that false view, and by a culture of silence from colleagues, even those who were not violent themselves.
The wardens' violence caused injury but its main aim was to "crush the will of trainees, to terrify them and make them feel powerless".
He said it was only through the commitment and persistence of the victims and the dedication of the police that enough evidence was gathered to paint the true picture of what happened there.
Toby Hedworth QC, defending Onslow, said either the leadership at Medomlsey was lacking, causing lower ranked officers to believe what they were doing was right, or the leaders were now going unpunished and it was only the "foot-soldiers" who were facing the consequences.
He said: "That regime is now being examined in the light of wholly different values and attitudes from those which pertained in the 1970s and early 1980s."
He said Onslow was the principal carer for his wife, and he had a much longer period of service working in prisons after Medomsley without any issue.
Caroline Goodwin QC, representing McGee, said he had many years of public service, adding: "He is a proud man and stands tall at every opportunity."
Simon Kealey QC, for Blakely, said he had worked with recovering drug and drink addicts for years after finishing in the prison service where he had an unblemished career.
The officer leading the investigation, Detective Chief Superintendent Adrian Green, said: “These men, who are all former prison officers, abused their position to cause immeasurable suffering and lifelong damage to their victims.
“We hope that their convictions and the sentences passed today provides victims and survivors of abuse at Medomsley with some comfort and a feeling that justice has been served.
“For more than five years, our dedicated team of investigators has worked extremely hard to investigate all reported incidents of abuse and to gather evidence to present in court.
“We have faced a number of challenges during the investigation due to the sheer scale of the enquiry, the nature of the offences and the time that has elapsed.
“When we launched Operation Seabrook back in August 2013, we could never have envisaged the huge numbers of men coming forward to report abuse while detained at Medomsley.
“We have had a further 89 victims and survivors come forward to us after the reporting restrictions were lifted last month at the conclusion of the third trial, bringing the overall number of victims to 1,765.
“It has taken a huge amount of courage for these men to tell police what happened to them and we have worked hard to ensure they are listened to and supported throughout the investigation and subsequent court process.”
Two other former officers, Alan Bramley, 70, and Brian Johnson Greenwell, 71, were both found guilty of one count of misconduct in a public office. They will be sentenced at a later date.
Onslow, McGee and Greenwell have since submitted appeals against their convictions for misconduct in a public office. These appeals are currently ongoing.