M51 or M-51 may refer to: M-51 (Michigan highway), a state highway in Michigan M51 highway (Russia) M51 (Cape Town), a Metropolitan Route in Cape Town, South Africa M51 Skysweeper, an anti-aircraft gun M51 MACI mine M51 SLBM, a French nuclear ballistic missile BMW M51, a 1991 straight-6 Diesel engine Sherman M-51, an Israeli modification of American M4 Sherman tank Eidgenössischer Stutzer 1851, a historical service rifle of the Swiss Army Messier 51, a spiral galaxy also known as the Whirlpool Galaxy Samsung Galaxy M51, a smartphone released in 2020