'H.M.S. Pinafore' is a comic opera in two acts, with music by Arthur Sullivan and a libretto by W. S. Gilbert. The opera ran for 571 performances, which was 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. The story takes place aboard the ship 'H.M.S Pinafore'. The opera's humor focuses on love between members of different social classes and lampoons the British class system in general. Pinafore also pokes good-natured fun at patriotism, party politics, the Royal Navy, and the rise of unqualified people to positions of authority. The title of the piece comically applies the name of a garment for girls and women, a pinafore, to the fearsome symbol of a naval warship.