The trio - along with clubbers at DeVitos nightclub in Arbroath who joined in during the incident - could potentially now face jail after they admitted charges of public indecency.
Forfar Sheriff Court heard that the three Marines took part in the incident in the club’s smoking area on 2 June this year, which was caught on CCTV.
The court heard Luke Bowen urinated in the mouths of fellow Marines Jordan Coia and Ben James.
Bowen then drank his own urine as well as that of others.
A fourth man, Craig Lynch, who is not in the military, then performed a sex act on another person during the incident.
However, despite admitting the charges none of the men will face being placed on the sex offenders register after the Crown accepted there was “no significant sexual element” to the crime.
Lynch, 42, of Aberdeen, James, 22, of Thirsk, Bowen, 25, of Chichester, and Coia, 22, pleaded guilty on summary complaint to a charge of public indecency.
Jacob Holt, 21, Ryan Fowler, 23, Michael Byrne, 26, all care of RM Condor in Arbroath, had their not guilty pleas to a charge of public indecency accepted.
It is understood those three men remain serving Royal Marines.
A court source said: “This is a massive embarrassment for the Marines - its not the image they want to give off.
“Initiations of some kind have existed in the military for decades but they want to eradicate this kind of behaviour, especially when it is in public as this was.”
Solicitor Nick Whelan, defending Coia, said: “This resulted in the ending of service for a number of these young men, including Mr Coia.
“What he thought would be a lifetime relationship with the military has come to an end after two-and-a-half years of service.
“The case has been hanging over these individuals and has prevented him obtaining employment as it is still pending.”
Nick Markowski, defending James, said: “He was also discharged from the Royal Marines.”
And Lynne Sturrock, for Bowen, added: “He’s been discharged and now lives with his parents.”
Sheriff John Rafferty deferred sentence on the four men for social work background reports and released them on bail meantime.