Four senior marines failed to stop assaults during an initiation-style ceremony, a court martial has heard.
Sergeants Richard Melia and Ian Spence, and Corporals Robert Wake and John Arnett each admitted four counts of failing to perform in their public duty.
The assaults included "reefing", where marines are struck with a belt or strap on bare skin, often on the bottom.
Sgt Spence also admitted pouring vodka in one junior colleague's wound.
The court martial in Portsmouth heard the four men failed without reasonable excuse to stop a number of junior marines assaulting each other on October 28 2014.
The assaults were carried out by others not involved in the hearing, the court heard.
'They did not stop it'
Judge advocate Robert Hill said: "This was a gathering of a number of ranks of marine. It was a gathering called for - but it wasn't advertised in advance - as an initiation.
"During the course of it, there was reefing of some of the junior members.
"The case against these defendants is that they are NCOs (non-commissioned officers) and they did not stop it."
The court heard Cpl Arnett, 33, previously of the Lympstone commando training centre in Exmouth, Devon, had since left the military.
Sgt Spence, 37, also formerly of Lympstone, was medically discharged from the military in July. He also admitted ill-treatment of a subordinate.
They were joined in court alongside fellow defendants 33-year-old Sgt Melia of the City of London marine barracks, and Cpl Wake, 30, of 40 Commando near Taunton in Somerset.
Sentencing is due to take place at the end of October.
