Were you aware that the United States Military Academy's Department of History teaches students to fire 1500s matchlock muskets? Conduct WWI-style trench warfare?
These are some interesting videos. The old lessons become relevant again surprisingly regularly: think of the SF guys in the early days of Afghanistan having not only to ride but to pack horses. Rigging a pack horse is an entirely separate skill set, once well known to the American cavalry.
The lessons of trench warfare can become relevant again quickly, if only for an afternoon: but if it does, remembering the old ways is the difference between surviving the afternoon and not.