I am a big fan of warships - battleships in particular - and I am interested in giving Grand Fleets a try. On w23 there are two versions - one for the "dreadnought era"(1890-1940) and one for the "battleship era" (1890-1950). Does that mean that the "battleship era" version has all the ships and rules of the "dreadnought era" version, plus more to cover WWII, or do you need to buy both if you want to play both WWI and WWII-based scenarios?