Joseph Isaacs, 40, has been found guilty at Taunton Crown Court of attempted murder after attacking 96-year-old D-Day veteran Jim Booth with a claw hammer and leaving him for dead.
Mr Booth suffered multiple head injuries after he was attacked in his home in Taunton in November last year.
Isaacs, of no fixed address, was on trial for attempted murder, which he denied.
He had already pleaded guilty to charges of grievous bodily harm with intent, aggravated burglary and a number of fraud charges.
Mr Booth was attacked after answering the doorbell to a cold caller who claimed to be a builder and offered to fix some broken roof tiles.
When Mr Booth refused, Joseph Isaacs pursued the older man through a passageway in his home, hitting him multiple times with it until he collapsed on the floor of his living room bleeding heavily.
Mr Booth was later told that one of the injuries on his arm showed that he had hit back.
During the war Mr Booth joined the Combined Operations Pilotage andReconnaissance Parties (COPP) and trained for covert beach explorations at a wartime military base set up on Hayling Island in Hampshire in 1943 under the instruction of Lord Mountbatten.
Mr Booth became a submarine pilot for the X-craft, tiny submarines that waited on the seabed for days at a time, at the age of 23.
Mr Booth was later awarded a Croix de Guerre military medal by the French for his gallantry.