Petrov served as the commander of a training battalion in the 1st Mechanized Brigade, before fighting in the Spanish Civil War, serving as a battalion commander in Dmitry Pavlov's tank brigade from October 1936 to June 1937.
Petrov kemudian bertugas sebagai komandan batalion pelatihan di Brigade Mekanika ke-1, sebelum bertarung dalam Perang Saudara Spanyol, dengan bertugas sebagai komandan batalion dalam brigade tank pimpinan Dmitry Pavlov dari Oktober 1936 sampai Juni 1937.