Arnold's owner realised he would not be able to climb to safety
The tables were turned when a dog, usually associated with saving people in distress, got himself into a spot of bother on the beach.
Arnold, a St Bernard-mastiff cross followed another dog down 130 steps to Whipsiderry beach near Newquay, but was too old - and fat - to climb back up.
As the tide came up the beach, Arnold's worried owner contacted coastguards.
After failing to haul the 15st (95kg) dog off the beach, an RLNI crew had to use an inshore lifeboat to save him.
Six Newquay lifeboatmen and coastguards used a fishing net to transfer Arnold into the lifeboat, which then ferried him and his very relieved owner to safety at Porth beach.
An RNLI spokeswoman said despite initial concerns about whether the huge dog would actually fit into the boat, it had a successful outcome and the elderly dog appeared none the worse for his ordeal on Monday evening.
It took a team of six to lift 15st Arnold into the lifeboat
Volunteer helmsman Ian Jepson said: "It's not the first time we have been called out to rescue a dog - but this was certainly the biggest.
"He was a big old boy and a bit grumpy, and being a dog owner and lover myself I really felt for him.
"We are always pleased to help whether it is on the beach or at sea, and whether it is a human or animal," added Mr Jepson.