Nazis had just torpedoed Winfred Polzin's landing ship.

"There was an awful jolt," he recalled recently from a rehab center in Cambridge, Minn., where he's fighting off an infection. "And a heck of a noise."

At 97, his memory scalpel sharp, Polzin flashed back 72 years to the month. He was 25, a sergeant from Rush City, Minn. He needed to act fast to dodge the fate of 749 fellow servicemen killed in those early morning hours of April 28, 1944.

Along the southern coast of England, American troops were conducting Operation Tiger — a secret, massive, 30,000-man dress rehearsal for the D-Day invasion of Normandy coming in June.

Things went awry when Nazi torpedoes struck two of the landing boats. Polzin used his bare hands to pry open an airtight door. Stepping past bodies strewn on the deck, he climbed over the railing, inflated his life belt and began crawling down a cargo net toward the dark water below.

That's when a panicked fellow soldier, who couldn't swim, suddenly "grabbed me around the head and down we went" — tumbling into the chilly English Channel.

Lessons gleaned from combat swimming school in London "came back to me right away. I doubled up, kicked my feet into his stomach, reached behind and pushed his chin" to gain separation.

Polzin tried to get the hollering and splashing soldier a life belt. "But he floated away," he said. "I can still see him."

A commander, disobeying orders to get his ship to port, insisted on one final search for survivors. Polzin was plucked from the water.

Less than six weeks later, Polzin landed on Utah Beach for D-Day and the beginning of the end of World War II. Today, he's one of roughly 12,000 surviving veterans of the 326,000 from Minnesota who served in the war. No one is sure how many of the nearly 300 survivors of the Operation Tiger fiasco remain alive.

"I thought it was just my brigade," Polzin said. "It wasn't for another 35 or 40 years that I learned that this Operation Tiger had 300 ships and 30,000 men. We were told we'd be court-martialed if we said anything about it."

His late brother, Orville, was in North Africa. When they bumped into each other later, "he bawled me out for not telling him what had happened," Winfred said. "But I didn't care. We had to keep it quiet."

Some details of Operation Tiger were declassified two months after the Normandy invasion but many of the stories were kept quiet for 50 years — leaving the chapter largely forgotten. In 1996, naval secretary John Dalton called the operation the "finest hour" for LSTs (Landing Ship, Tank) — vessels like the one Winfred Polzin crawled off 72 years ago.

"The next morning, the bow was sticking up but the stern had sunk to the bottom," he said.

Polzin was the second of five sons born near Watertown, S.D., and his family lost its farm during the Depression. He moved east to Minnesota in 1936 and found work as a farmhand in Rush City before joining the U.S. Army in 1942. He served in major European theaters, including Sicily and France.

As a sergeant with the 478th Amphibious Truck Co. of the First Engineer Special Brigade, he was in charge of 50 men and 24 truck-boat hybrids designed in 1942 by General Motors Co. With powerful pumps that could purge water, they proved to be game-changing cargo and personnel transports.

"We used them at the invasion of Sicily," Polzin said. "You could inflate and deflate each tire one at a time if the sand was bad on the beaches."

Before training in North Africa on the so-called Ducks (officially DUKWs in military and GMC acronym parlance), "I'd never heard of it or seen it," said Polzin. "It was 91 percent land truck and they built a hull around it."

A few years ago, Polzin met a collector of 80 World War II vehicles near Spooner, Wis., including one of the amphibious vehicles he remembers so well.

"There is a certain way to step into the driver's position and he knew it," said Paul Dorow, Polzin's son-in-law. "At 90, he climbed down a 10-foot ladder and swam the thing in a lake up there."

After the war, Polzin farmed near Braham, worked at the ammunition plant in Arden Hills and did aluminum welding. His wife, Dallas, died in 1986, leaving three daughters. Polzin has nine grandchildren and 11 great-grandkids. One of the grandsons, Erich Dorow, was a staff sergeant deployed by the Air Force to Afghanistan, where he called in air support to danger spots.

"It's a unique situation to have a World War II vet and his grandson, who is also a veteran, in the family at the same time," Paul Dorow said. "I don't think it happens very often, simply because of the time span. We're very proud and grateful that both of them made it home safe and sound."

Polzin said his landing ship was toward the end of line in 1944 when it took the torpedo strike from the Nazis.

"I was always the last in the line for anything," Polzin said, "but always first for something to happen to."

Curt Brown's tales about Minnesota's history appear each Sunday. Readers can send him ideas and suggestions at mnhistory@startribune.com. A collection of his columns is available as the e-book "Frozen in History" at startribune.com/ebooks.