The men, two of whom were superintendents in the brigade, were charged after one cadet came forward to say he had been abused.
The cadet's claim led to a flood of former members making similar allegations and a police team of 25 detectives being assigned to the case.
Officers flew to Australia, Canada and the Falkland Islands to interview former St John cadets. By the end of the investigation police had identified more than 80 victims all under 16 - the majority of whom were St John members.
The ring was headed by the man in charge of the Farnborough Division of the Brigade in Hampshire, 64-year-old Superintendent Leslie Gaines.
Charges
Gaines, from Bognor Regis, in West Sussex, has already pleaded guilty to 11 charges of indecent assault, and has also admitted five charges of buggery and one attempted buggery of St John cadets.
Gaines's successor as head of the division, Colin Hawyes, 51, from Farnborough, was convicted after a trial.
Hawyes, a contracts manager, was found guilty of three charges of indecently assaulting boys.
Gaines's lodger, 69-year-old Eric Attfield, from Aldershot, was found guilty of two indecent assaults on boys.
He was also convicted of one offence of buggery and two attempted buggeries, but was cleared of one indecent assault and one buggery.
Judge Patrick Hooton has said he will sentence the men, who are in custody, on 4 December when pre-sentence reports have been prepared.
Nine-year-old victims
For the prosecution, Stewart Jones QC told Winchester Crown Court that some of the boy cadets were as young as nine.
They had been sexually abused on Brigade camping trips and at Gaines's flat, which had been turned into a "mini youth club".
Although not a member of the Brigade, Atfield had gone on camping trips with them and visited the Brigade hut.
Quarter-century of offences
Some of the offences were more than 30 years old, having all taken place between the mid-1960s and the late 1980s, Mr Jones said.
The abuse victims who gave evidence before the court were all in their late 30s and 40s.
Mr Jones told the jury: "All the young boys - as they were then - came to know the defendants through Leslie Gaines.
"For many years Gaines was active in the Farnborough Cadet Division of the St John Ambulance Brigade. And from 1964 to 1983 he was the District Superintendent."
He was responsible for organising and supervising activities from first aid to camping expeditions and from his flat produced and distributed a fortnightly newsletter.
"This was written mainly by Leslie Gaines and printed with the help and contributions by some of the boys.
"Boys came alone and in groups to play snooker and because Leslie Gaines allowed them to smoke. Sometimes there were fizzy drinks and crisps and so on.
"Through their connection with Leslie Gaines the defendants met the boys and we say the boys were abused in various ways by them."
The jury cleared driving instructor Barry Hyam, 44, from Farnborough, of four charges of indecent assault on boys.
A 41-year-old former cadet from Basildon, Essex - who cannot be named for legal reasons - was cleared of an indecent assault charge.
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