"I got the highest mark," he said.
It also saved his life, he said.
He had put in a transfer from a boat, which was later destroyed by the Germans.
"If I didn't study for that test, I would have been on that boat. You're talking about fate," he said.
Remembering the sight of New York harbor as he returned to the United State when the war in Europe was over he said, "The prettiest thing I ever saw was the Statue of Liberty."
When he was discharged from the Navy, he took up a career as an arborist in Texas.
He eventually made his way to Maryland, and worked for Johns Hopkins Hospital as a ground supervisor from 1961 to 1971.
He then went on to work as a grounds manager at General Electric in Columbia.
He has two children, Leah Griswold Rudolph and Scott Griswold.
His wife, Kathryn Griswold, a nurse who graduated from Johns Hopkins University, died in 1998 at the age of 72.
Among his friends at Charlestown retirement center are six other D-Day veterans, which he said provide him with camaraderie.
"It's a buddy system that's hard to describe," he said.