In 1779 Ewald's company was involved in British operations to capture key American defenses at Stony Point, New York. It was not involved in the American response, a raid by Brigadier General Anthony Wayne that captured more than half the British garrison. Most of 1779 was spent on guard duty, until December, when his unit, specifically requested by Generals Clinton and Cornwallis, was selected for the expedition to take Charleston, South Carolina. His company was again in the vanguard on the march from the landing place to the city. At one point he used a ruse to reconnoiter an enemy position on the Stono River. After waving his handkerchief, he approached an enemy outpost, and inquired whether the unit, which he ascertained to be Pulaski's Legion, had a supposed acquaintance of his serving in it. During the conversation he carefully noted the surrounding features, before returning to his unit. This action drew praise from General Clinton. After the successful siege, Ewald's company returned to New York with General Clinton, leaving Cornwallis the task of taking control of South Carolina. He spent the remainder of 1780 on guard duty around New York, until he learned in December that his company had been chosen to be part of Benedict Arnold's expedition to Virginia.