Strategos is a military wargame developed by Charles A. L. Totten for the United States Army, and published in 1880.
Charles A. L. Totten, ca. 1875
A wargame, generally, is a type of strategy game which realistically simulates warfare. A professional wargame, specifically, is a wargame that is used by military organizations to train officers in tactical and strategic decision-making, to test new tactics and strategies, or to predict trends in future conflicts. This is in contrast to recreational wargames, which are designed for fun and competition.
A wargame at the US Naval Postgraduate School (June 2018).
A reconstruction of the wargame developed in 1824 by Reisswitz
The Navy Electronic Warfare Simulator (1958).
A wargame at the US Naval War College. This photo was taken in the 1950s, but strongly resembles the wargames played in the 1930s.