M45 or M-45 may refer to: In science: Messier 45 (M45), an open star cluster also known as the Pleiades 45th known Mersenne prime M45 genetic marker, a genetic marker on the Y-chromosome Yahoo!'s M45 supercomputing cluster In transportation: Infiniti M45, a luxury car M45 motorway, a motorway in England M-45 (Michigan highway), a state highway in Michigan In firearms and military equipment: Carl Gustav M/45, a Swedish submachine gun M45 SLBM, a French submarine-launched ballistic miss… (More on M45)