In the 1950s, he appeared as Sheriff Andy Anderson on Rod Cameron's syndicated western-themed television series, "State Trooper". Armstrong made four guest appearances on "Perry Mason" during its nine-year run on CBS: in 1961 he played the title character and murder victim Captain Bancroft in "The Case of the Malicious Mariner"; in 1962 he played defendant Jimmy West in "The Case of the Playboy Pugilist"; and in 1964 he played murderer Phil Jenks in "The Case of the Accosted Accountant," thus becoming one of only eleven actors to hit the Perry Mason trifecta, playing victim, defendant and murderer.