High Quality Content by WIKIPEDIA articles! HMS Isis launched in 1819 was ordered in 1811 as a 50-gun two-decker of the fourth rate Salisbury class, but was redesigned while building, being lengthened on the stocks by 11 feet, and cut down by one deck to produce a spar-deck frigate, that is, to carry extra guns on the spar deck which linked the forecastle to the quarterdeck.