A man who attacked a 96-year-old D-Day veteran with a claw hammer has been given a 20-year extended sentence after being found guilty of attempted murder.

Joseph Isaacs, 40, attacked Jim Booth at the older man’s home in Taunton, Somerset, after he became enraged when Booth turned down his offer of cheap building work.

Facebook Twitter Pinterest Joseph Isaacs: he claimed he had gone to Jim Booth’s house to get money for food. Photograph: Avon and Somerset police/PA

Booth, a Royal Navy veteran who played a key part in the success of the D-Day landings and went on to clear mines in the Mediterranean after the war, tried to escape by retreating into his house but was pursued by Isaacs, who hit him again and again with the hammer.

Isaacs, of no fixed address, denied intending to kill Booth and claimed he had gone to the house to get money for food. A jury of seven women and five men at Taunton crown court found him guilty of attempted murder after less than two hours of deliberation.

Isaac had already admitted causing grievous bodily harm with intent, aggravated burglary and six allegations of fraud in relation to the attack at an earlier hearing.

Booth, a great-grandfather, was left with multiple skull fractures and lacerations to his head, hands and arms after the attack on 22 November.

In his victim impact statement, which was read to the court by the prosecutor Rachel Drake, Booth described the ongoing effects of the attack, saying he now suffered from severe head pain ranging in severity from “just about coping to having to lie in bed all day”.

He said there was rarely a day when he was not affected by the head injury, while the injuries to his hands had affected his organ-playing.

He said he had always been very involved in his four grandchildren’s lives and more recently his two great-grandchildren’s, but he was “no longer well enough to be as hands on as I would like”.

The judge David Ticehurst said Booth was an “extraordinarily remarkable gentleman” whom Isaacs had “savagely attacked with a claw hammer which you took with you for that purpose”.

He said: “It was a brutal and utterly senseless attack on him. Jim Booth was 96 years old, living on his own but with remarkable independence and vigour. The effect upon him and his family has been devastating, as is clear from Mr Booth’s victim impact statement. His daughter Victoria Pugh also spoke of the effects of your crimes on them.

“That your crimes have had such a devastating and damaging impact on them is something you should reflect upon in the years before you.”

Ticehurst said Isaacs had committed the crime for a “paltry” amount of money and then shown an apparent lack of remorse or concern. He said he considered Isaacs to be dangerous and therefore to meet the criteria for an extended sentence.