HELP: Sgt Mark Langworthy, Marine Chaz Ellis-Stansfield, Helen from Tesco and Cpl Andy Godfrey.
Andy Godfrey and Chaz Ellis-Stansfield were in the Tesco Braunton store when a man allegedly took alcohol without paying.
Corporal Godfrey and Marine Ellis-Stansfield are part of the Commando Logistic Regiment and often provide security during operations and for public events.
They told the Journal the thief cycled off towards the Tarka Trail which runs alongside RMB Chivenor.
They decided to return to the base and wait for him.
Minutes later they spotted him cycling along the Tarka Trail towards the roundabout at the military base's entrance.
Cpl Godfrey, 25, from Torbay, said: "We crouched in a bush and lay waiting for him. As he came past we jumped on him.
"We restrained him with an arm lock and held him down."
Braunton police were called and they arrested the man.
Cpl Godfrey said: "In our type of job there are situations that you can't just let happen. If we can help others and do our bit for the community then we will.
"We were just in the right place at the right time and we were not prepared to let this go."
Marine Ellis-Stansfield, 25, from Norwich, said: "The opportunity was there to help out. We put the community before our own safety."
Sgt Mark Langworthy, of Braunton Police, said: "We want to thank the marines and give them credit for their actions.
"The police have always had great links with Chivenor. The staff on the base are always happy to offer assistance and help in whatever way they can.
"This could be a good result and just goes to show what can happen when we work in partnership."
● A 39-year-old man from Barnstaple appeared in North Devon Magistrates' Court on Tuesday and indicated a plea of guilty to stealing five, one-litre bottles of vodka from Tesco on Monday January 25.
He was remanded on bail and the case was adjourned until Thursday February 18.