A set of sixty Fog-of-War cards is provided with Command Decision, Test of Battle. You might ask, "What are Fog-of-War cards?" and "What is the purpose of the Fog-of-War cards?" The answer is--these cards have more than one rationale. Two of the key reasons are, "stuff happens" and "unpredictability."
In almost any reading of military history there is a great deal happening on the battlefield, and a number of combat's more interesting anecdotes are not easy to explain. Fog-of-War cards allow for this without adding many extra rules. As with any set of rules, you must also quantify different factors and elements. Once these are quantified everyone knows exactly what these factors are. In combat, none of these factors are absolute--with Fog-of-War cards we can revisit this unpredictability.
As stated above, with Fog-of-War cards cards, we can add the "fog-of-war" without adding any extra rules. You might wonder, "Can a card decide the outcome of a battle?", and the answer is, of course, just like a die roll can decide a game. Having said that, no Fog-of-War card will guarantee victory, but the correct application of these cards will help achieve victory.
In the future Command Decision: Test of Battle plans on expanding the range of these cards. There will probably be a subset for most nationalities which will include the idiosyncrasies and tendencies of these armies.