Jock Moffat, 95, who is said to have fired the torpedo that hit the Bismarck's rudder in 1941, said he has already cast his postal vote for No in Scotland's independence referendum.
The veteran, from Dunkeld, in Perth and Kinross, joined Scottish Conservative leader Ruth Davidson, to make the defence case for the union.
Mr Moffat was among the audience gathered in Perth as Ms Davidson argued that the UK's Armed Forces "embody the very best of our union", and attacked the SNP's plans for a Scottish defence force.
He said: "Pals of mine who didn't make it...I have a feeling that if I had gone to a Yes vote I would have betrayed them."
The former Royal Navy Fleet Air Arm pilot also hit out at Alex Salmond and Nicola Sturgeon, adding: "I think the heads of the SNP is not quite true in what they say. I have a feeling that they are trying to find sources of money which aren't there.
"They're very clever - they come across on the television and they may sway some of the people, but I hope that the people will vote from an economic point of view and not from the heart."
Mr Moffat said he hoped that defence resources such as new aircraft carriers would be used to "go to the rescue of countries that are struggling".
His views echoed Ms Davidson, who used her speech to highlight the work of British forces across the globe, including humanitarian efforts in the Philippines following the typhoon last year, and work in the Caribbean to tackle drug traffickers.
Drawing on the forces' long history, Ms Davidson said Mr Moffat's example told her that "there are bonds of history and geography across our small island that go very, very, deep".
She said: "Those bonds will weaken if we don't keep the United Kingdom in two weeks' time. And the strength and the moral might of our Armed Forces will weaken too.
"And it's not just us who will be the poorer for that, it's our allies and it's people right across the world who have over the last century, been grateful for the courage of Jock, Bill (Bill Holden, a D-Day veteran) and the millions of others who have served under our flag."
Ms Davidson continued: "The experts, the former generals and the academics have all made it crystal clear: the Nationalists' plans for our Armed Forces are utterly insufficient and may end up costing us all more for so much less."
The Tory leader hit out at defence plans for an independent Scotland outlined in the SNP administration's white paper.
"Alex Salmond envisages an independent Scotland starting out with just 3,500 regular army personnel and a back-up of only 1,200 reservists. Why would our young recruits join that?" she said.
"Faslane would stay, he says - despite the fact that, as an independent Scotland's main port, it would be on the wrong side of the country to help guard and patrol our oil fields in the east.
"And on the shipyards, we know that the very future of the industry would be threatened. It is just a fact that the UK does not build complex warships in foreign countries."
Jimmy Sinclair, of Kirkcaldy, one of the last surviving member of the Desert Rats, rejected Ruth Davidson's claims about defence.
Mr Sinclair, who turned 102-years-old in August, said: "The No camp must stop playing politics with Scotland's fallen war heroes - it's totally unfair, misrepresentative and just plain wrong of them.
"This is really offensive stuff - sacrifices made on the battlefield of the past wars are respected by everyone.
"I will be voting Yes in the referendum, because I am a patriot and I believe in Scotland's future. With a Yes vote and independence Scotland will always get the governments we vote for."