He ended up as one of the first radar operators on a British submarine, his shore base in Malta, his 25 patrols from there helping to cripple the Axis supply lines to North Africa and hasten Hitler's defeat.
Sitting in his Richmond dining room, the still-dapper 90-year-old tells his war story in a matter-of-fact way and sprinkles it with the natural humour of a Londoner.
He says he was "about 17" when he joined the Royal Navy and was soon being trained in Scotland and England.
"Radar was just coming in and it was quite secret."
Early in 1942 he was assigned to the U-class submarine HMS Ultor, one of 49 that served in World War II.
Small at 58 metres - think of two railway carriages, Mr Bishop says - they carried a crew of 27 to 31.
Originally designed as training vessels for surface ships to practise their submarine attacks on, they were slow, could only dive to 80 metres, and had crowded living conditions, but their smallness proved suitable for the Mediterranean.
"They had a lot of drawbacks . . . but they were quick diving, and easy to maintain."
They had to surface at night so that their diesel motors could charge the batteries used for underwater travel and during that time it was Mr Bishop's job to share radar duties with one other crew member, each working one hour on, one hour off, watching for enemy ships and planes.
He says the equipment was primitive and "I think the skipper had more faith in it than I did, actually".
Once submerged the radar was inoperative and he was assigned to other duties - maybe going on the ship's wheel or cooking the meal. Watches were four hours and "you didn't get much sleep".
HMS Ultor was painted deep blue because on a calm day submarines were visible 20 metres under water to patrolling aircraft looking down on the clear water. It was part of the 10th Submarine Flotilla, which fought out of Malta during the legendary siege when German and Italian bombers relentlessly pounded the island in an unsuccessful attempt to subdue it ahead of an Axis invasion that never came.
Sometimes the Ultor submerged at its berth to avoid bombing raids. Between patrols the crew lived in an old stone building close to the shore.
"There were more bombs dropped on Malta than on London during the Blitz," Mr Bishop says.
Having already experienced that bombing as a teenage Civil Defence volunteer before joining the navy, he jokes that "I think the Germans had it in for me".
The Ultor could be at sea for as little as 10 days or as long as three weeks, depending on how long it took to find targets for the four torpedoes it had in its tubes, and the four it carried to reload with.
"When you'd expended those, you might as well go home."
Its mission was to sink ships supplying the Axis forces in North Africa. It accounted for 28, more than any other British submarine, Mr Bishop says, and it was often under attack itself.
Enemy warships would pass overhead, their engines thrumming like an express train, and then the submariners would wait for the sound of depth charges exploding.
That's the hardest part, to see if they've thrown anything over the side or not. Half the time they probably dropped the depth charges miles away."
Nine British U-class submarines were lost in the Mediterranean. The Ultor escaped unscathed.
Mr Bishop says he was too young to feel much fear, except once. On his last patrol they sank a supply ship which had a destroyer and aircraft escort and then found there was another ship nearby also escorted by destroyers and planes. The two groups joined up to hunt the Ultor, which "really got a hammering" while it manoeuvred underwater.
"I can remember thinking, ‘What the hell am I doing here?'."
He is more at ease talking about living conditions: canned food day after day, with 12 tins of M and V (meat and vegetables) a standard meal for the crew, one toilet for 15-18 men, with no privacy and a view of the turning propeller shaft, not enough water to wash.
After the war Mr Bishop trained as a compositor in London and, intrigued by the stories a Kiwi workmate from Canterbury told, brought his wife and daughter to New Zealand in 1953. He worked on the Otago Daily Times, went to Tasmania for a year, came back to New Zealand and was employed by the then Nelson Evening Mail for the rest of his working life.
He's been an RSA member and has attended many Anzac Day parades. He says when he thinks about the war, it's the "wicked waste" that comes to mind. He's not sure about tomorrow.
"I'll see how I feel. I'm not good at standing for long periods."
The interview over, a framed text on the sideboard catches my eye.
Dated September 1944, it's a citation awarding Able Seaman John Bishop the Distinguished Service Medal "for courage and skill serving in war patrols on HMS Ultor". He went to Buckingham Palace with 10 of his shipmates equally honoured, to get his medal from King George.
He hadn't thought to mention it.