Battle of Naseby
Cromwell's double regiment was later split into two regiments (Sir Thomas Fairfax's and Edward Whalley's), which became the nucleus of the New Model Army's cavalry. Shortly before the Battle of Naseby, Cromwell was reappointed Lieutenant General of Horse in the army, and later became its commander. "Ironsides" seems to have become the term for all cavalry in the army, regardless of their origin.