A bruising, hard-hitting defenceman, Armstrong anchored the Boston blueline for every one of his 542 career NHL games after graduating from Stratford in junior hockey. He never rushed the puck, got into plenty of fights, and made it to the Stanley Cup finals twice, losing to Montreal in 1953 and again in 1957.
He played junior in Stratford in the late 1940s until breaking in with the Bruins in 1950-51. The following year was entirely with the farm team in Hershey until the playoffs when he was called up as a stopgap measure and played in five games. Amrstrong spent most on the next dozen years in the NHL.
In 1961-62, he started the season, as usual, in Boston, but was demoted after nine games. Two years later, he retired.