Munro of Foulis progressed quickly through the ranks, advancing to Captain, then Major and finally Lieutenant Colonel in Mackay's Scottish Regiment. In 1628 the Danes sent several Scottish regiments including those of Lord Spynie and Donald Mackay's (which included Munro's company) to fight in the Battle of Stralsund. Under Danish leadership the regiment was treated disgracefully, being forced often to sleep in the streets. When Alexander Leslie arrived from Pomerania with more Scottish, Swedish and German volunteers in July, he was also awarded governorship of the city. He was keen to show his admiration for his countrymen and amalgamated those he had brought from Sweden into a single fighting force with the Scots already in the city. He used the mixed Highland and Lowland contingent in a spectacular assault on the enemy which finally broke the siege. As Robert Monro recorded: