Developing realistic models has proven to be somewhat easier in naval simulations than on land. One of the pioneers of naval simulations, Fletcher Pratt, designed his "Naval War Game" in the late 1930s, and was able to validate his model almost immediately by applying it to the encounter between the German pocket battleship "Admiral Graf Spee" and three British cruisers in the Battle of the River Plate off Montevideo in 1939. Rated on thickness of armour and gun power, "Graf Spee" should have been more than a match for the lighter cruisers, but Pratt's formula correctly predicted the ensuing British victory.