Lightning: D-Day was the second of the initial offerings in the Lightning series of wargame-like card games published by Decision Games.
Like Lightning: Midway, the play is too abstract to be considered any kind of simulation, but much too imbued with military arcana to be considered a simple military-themed card game.
Like its sister game it shares the problem of rules that are too succinct for the task. I didn't find it too difficult to figure out how to play, but many did and the game's official Q&A is longer than the main game rules. As with Lightning:Midway this is mostly because too much is assumed and not because there are any particular flaws in the game rules. Everything is a clarification, rather than a change.
Despite what the rules say, there are actually five, not four, different kinds of cards. Unlike Lightning:Midway, which has no explicit time limit, Lightning: D-Day is a 5-turn game. The turns are tracked using five "Turn Marker" cards which have varying special effects (such as "Wading Ashore! All Allied Attacks get -1" for Turn #1). Each card also informs the players how many cards to draw to prepare for the following turn.
There are a pair of "Country" cards which summarize the sequence of play and say who goes first (The Germans).
There are five Beach cards which are simple zone markers for (from East to West) Sword, Juno, Gold, Omaha and Utah beaches.
These dozen cards are set aside at set up and don't form part of the players' hands, which comprise the remaining 98 cards (49 each). The fighting portion of the decks are made up of Force Cards which represent major formations such as the 1st Infantry Division. These are identified by beach and are divided up by beach, shuffled and placed face-down at each beach as "inactive" units. During play these are turned face-up in order to fight. Each has a combat strength and most have some special powers or conditions as well.
The leftover cards are all "action" cards which modify the game in various ways.
A turn consists of fighting a battle at each beach in turn, comparing the respective combat strengths as modified by various action cards. As the allocation of force cards is fairly scripted the players' main tools for influencing the battle comes down to the three dozen or so Action cards that can be played, for the most part, on any beach. Winning battles generally results in discarding force cards and Allied victory is measured by how many beaches have been completely cleared of German force cards (active or inactive). In order to win the Allies must clear at least four beaches, which is considered the historical outcome. I presume that, in game terms, Omaha beach was not cleared. Clearing three beaches is a draw, while the Germans win if the Allies clear two or less.
Playing the entire invasion takes about 30 minutes, making this another good filler game for wargamers once they have worked through the rules issues.