During World War II, she worked at Vickers Armstrong as secretary for Barnes Wallis and assisted him with his famous experiments to make a bouncing bomb to destroy German dams. Wallis would catapult wooden models across the water, which Gentry would then row out to retrieve. She rowed him out on Silvermere lake and took charge to ensure that they did not capsize, saying "Sit down Wallis! You'll have us both in the water, and I'm in charge of this boat!".