A Second World War veteran is marking the 70th anniversary of an act that led to him receiving the Distinguished Service Medal.

On March 7, 1945. using the earliest form of radar, Tom Simpson located a German U-boat.

It was a dark night on the North Atlantic, Simpson, who was a 23-year-old seaman at the time, was manning the radar on HMCS La Hulloise — a Canadian frigate.

She was patrolling the St. George's strait between Wales and Ireland when Simpson detected two images on the screen.

One image showed a buoy, but the other was the exhaust snorkel of a German U-boat or submarine waiting to attack.

But when Simpson told an officer about what he spotted, the officer didn't believe him.

"He said, 'oh, you're seeing gremlins,'" remembers Simpson, who is now 93 years old. "I said, 'gremlins, my ass.'"

Simpson said he was ready to throw the officer overboard when their captain intervened.

It ended up Simpson was right. A couple of hours later, with help from two other ships, the U-boat was sunk.

"The next thing you know there were bodies coming up," said Simpson.

Hundreds of lives were potentially saved that night — HMCS La Hulloise had a crew of 150 and other ships were in the area. As a result, Simpson was given the Distinguished Service Medal.

Saturday marks the sinking's 70th anniversary.

It was an experience that would haunt Simpson for years to come, and to this day.

"After yes ... I had qualms sending 40 to 50 men to their deaths," he said. "I had to see a psychiatrist for years. Even the last couple of years, I had to go and see her."

He said he has since made peace with the experience, knowing the U-boat had been actively sinking other ships.

Simpson received the Distinguished Service Medal in 1946. He was one of only 114 Second World War vets to receive the honour. He is the last surviving recipient, according to his grandson.

He has some advice for politicians and military leaders of today. Simpson said in order to bring peace to a turbulent world, people should be spending money to help developing nations become self sufficient, rather than on instruments of war.

Tom Simpson Medal

Tom Simpson, right, received the Distinguished Service Medal in 1946. (Submitted by Ronald Simpson)