In 1650 a Scottish army under Leven and Leslie was in a commanding position over an English force under the brooding Cromwell that was weakened and demoralised by a string of setbacks. Victory seemed certain for the Scots.
However, the ultra-purist Covenanters held sway over the conduct of Scottish strategy. On the very eve of battle they called for an ideological purge, which resulted in the dismissal of some 80 of the most experienced Scottish officers, and many of the rank and file.
Cromwell, outnumbered and holed up in Dunbar, spotted an opportunity presented by the disarray and uncertain positioning of the superior Scottish forces and struck a master-blow. A night attack by his cavalry broke the Scottish line and rout ensued, with minimal English casualties. Cromwell had plucked an unlikely victory from the jaws of defeat, exploiting to the full his opponents' ineptitude.