S23 may refer to : * S-23 (drug), an investigational selective androgen receptor modulator * S23: Do not breathe gas/fumes/vapour/spray (appropriate wording to be specified by the manufacturer), a safety phrase in chemistry * S23-Wiki, a project giving statistics about wikis * 180 mm gun S-23, a Soviet heavy gun of Cold War era * , a swamps and tall-herb fens community in the British National Vegetation Classification system * Chilean submarine Hyatt (S23), a 1973 Oberon-class submarine in the Chilean Navy * HMS Repulse (S23), a 1967 British Royal Navy's Resolution-class ballistic missile submarine * Patent Reform Act of 2011, America Invents Act, a bill introduced in the 112th United States Congress. * USS S-23 (SS-128), a 1920 S-class submarine of the United States Navy This dis