H.M.S. Pinafore, or The Lass That Loved a Sailor, is a comic opera in two acts, with music by Arthur Sullivan and a libretto by W. S. Gilbert. It opened at the Opera Comique in London on 25 May 1878 and ran for 571 performances, the second-longest run of any musical theatre piece up to that time. H.M.S. Pinafore was Gilbert and Sullivan's fourth operatic collaboration and their first international sensation.
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