"William Shirley, Governor of Massachusetts, was gifted with great political sagacity. His military ability, though not of a high order, commands respect because contrasted with the obstinate adherence to traditional methods, the blundering and inefficiency of Braddock, Loudoun and Abercrombie. He clearly saw that only by the capture of Louisbourg could safety be insured New England, and, like Cato of old, he successfully impressed it upon the councils of the commonwealth that this Carthage must be destroyed. Some of the prisoners taken at Canseau, when exchanged, brought from Louisbourg reliable description of its fortifications and information that disclosed supposed vulnerable points. This fortress had been perfected in all the defences then known to military art, at a cost to France of thirty millions of livres .Over one hundred guns, mostly of heavy calibre, were mounted in the various batteries, and six months' provisions for the garrison were kept in store. An English officer familiar with the works wrote that an army assaulting them would have the same prospect of success 'as the Devils might have in storming Heaven.'" [Source]
See another map of Louisburg and vicinity circa 1745 here.
A distant Richmond relative, Sylvester Richmond participated in the Siege Of Louisburg:
As written here, "Only the mutinous condition of the garrison in the fortress made its capture possible."