Barry Froggatt and Barbara Lavery both drowned in Hoe Lake
An inquest heard that Barry Froggatt, 75, and 76 year old Barbara Lavery both drowned when the silver Peugeot car slipped into Hoe Lake in Plymouth last August.
The hearing was told they had been taking the car for a test drive when the double tragedy happened.
Mr Froggatt was a former lorry driver with many years driving experience.
The silver Peugeot slipped into Hoe Lake
I couldn't get deep enough to get to the front of the car
Eye witnesses said the car had "reversed and overturned in the lake."
Former soldier Paul Brain dived into the water to try and save the pair.
He armed himself with a hammer in a vain bid to smash the car windows to free the trapped couple.
They took the car for a test drive
He said: "I couldn't get deep enough to get to the front of the car. I couldn't open any doors and I tried to smash the windows. I didn't realise how deep it was."
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Grandfather Mr Froggatt, who had been driving the car, was said by his family to have loved Barbara "to bits."
They praised would be rescuers for "their brave attempts."
Eyewitnesses said the car had "reversed and overturned in the lake"
Mrs Lavery's family said she was a "fine gregarious woman with a vibrant hunger for life."
They called her "nanny purple"' and also praised rescue attempts calling them "heroic instincts."