 Beginning in 1956, he added to his repertory the roles of Sergeant Bouncer in "Cox and Box", the Usher in "Trial", the Boatswain's Mate in "Pinafore", and Samuel in "The Pirates of Penzance".In 1956 Cook began to play the role of Giorgio in "The Gondoliers", while also serving as understudy for the principal baritone roles.He also took on the role of Scynthius in "Princess Ida" in 1957, and the roles of Go-To in "The Mikado" and Sergeant of Police in "Pirates" in 1962.