Jean-Baptiste de Couagne was one of two resident assistant-engineers which came to build Fortress Louisbourg, the other was Boucher. Couagne had come down from Montreal and reported to Louisbourg in 1717, the year in which construction started. These assistant-engineers oversaw the site work during the summer; during the winter they worked on their paper work. Couagne reported to Verville. Like Boucher, Couagne was adept at surveying and the making of maps and plans, many of which have survived and have become collectors items.
In August, 1715, we see that Couagne was busy at Port Toulouse (St. Peters) helping in the building of its fortifications. He had earlier carried out surveys around the Great Bras d'Or and the north shore with a view to convincing the mainland Acadians to came and settle in Cape Breton. On these reconnoitering trips about Cape Breton the 28 year old Couagne had two older Frenchmen with him, two familiar with the territory: the 47 year old Indian fighter, Hertel and the 40 year old privateer, La Ronde.
Couagne was particularly adept at surveying and the making of maps and plans. It should be noted that many of the surviving plans of the Louisbourg fortifications, while credited to his superiors, Verville and Verrier, were, in fact, drawn by Couagne.
We have also determined from the records that Couagne was married at Louisbourg on September 28th, 1720. His wife died during 1733, and he, himself died on January 22nd, 1740 at Louisbourg.