There were some interesting disparities between the armies tha | United Celts

There were some interesting disparities between the armies that drew up on September 3rd, chiefly amongst their cavalry. The English horse generally had larger mounts, and were very heavily armed, including with pistols which they would fire at very short range prior to charging into a unit. Scottish horsemen however had smaller horses and were less well armoured. Generally the Scots had better manoeuvrability but were inferior in close combat. The Scottish army numbered some 8-9,000 infantry, 32 guns and 3,000 horse with the English fielding 7,500 foot, 22 guns and 3,500 horse. Neither side made extensive use of their artillery due its immovability.

The night before the battle in the words of a Scots soldier was 'drakie nycht full o' wind and weit' and these adverse weather conditions hampered both armies as they tried to position against each other. The Scots commanders were unanimous in their desire to attack the weakened English army but historians debate as to what Cromwell's intentions were. Cromwell sallied out of Dunbar but some argue this was to attack at dawn and some argue he was forming a rearguard to cover his escape down to England. Between both armies flowed the Broxburn and at 4am English dragoons rode over its three crossings and drove back the Scottish Pickets, taking them by surprise and causing panic. The english launched a series of assaults across the Scottish lines, in most cases breaking through only to be thrown back by determined Scottish counterattacks. Heavy rain, thick smoke and morning fog made situational awareness for all commanders involved nigh impossible and the battle hung in the balance with reserves holding back, allowing pockets of fighting on the coastal plain to prevail.

The deciding moment of the battle came however when Cromwell's own Lord General's Regiment flanked the Scottish army crossed the Broxburn, singing Psalm 117:
O praise the Lord, all ye nations:
praise him, all ye people.
For his merciful kindness is great toward us:
and the truth of the Lord endureth for ever
This heavy cavalry formation smashed into the as yet inconclusive melee. This caused the Scots to collapse but at about 7am but many units conducted a brave fighting retreat, screened by cavalry towards Haddington. The English took some 5,000 Scottish prisoners, marching them down to Durham where many died on the way, with mass graves being unearthed in 2015, others being deported as indentured servants to English colonies. In comparison to Cromwellian war crimes in Ireland the English occupation of Edinburgh was benign and promised its citizens that no harm would come to them. The Scots leadership broke down at this point in a blame game, largely in relation to the purges of more experienced officers prior to the war, with radicals saying the defeat was punishment by God for not purging enough 'Engagers' (support for a royalist compromise' whilst some blamed the purging of these seasoned officers for the defeat. Dunbar allowed for Cromwell to, after a number of other engagements at Hieton, Inverkeithing and Worcester to occupy Scotland under English military rule.