D-Day (1961B) is a rule revision of the first edition of D-Day (1961A) (see separate version description). It perhaps should be called D-Day 1962 (some components are (c) 1962) but the designation "1961B" has become enshrined and will be used here. The only differences from DD61A were in the accompanying documentation (Instruction Folder [i.e., rules], Reference Folder, Combat Factors Card, and Combat Results Table). It was introduced without obvious fanfare -- apparently Avalon Hill simply began substituting the 61B components for 61A in new games shipped after some date. This must have created some interesting communication problems between players in the early days of Play-By-Mail!
As far as the game concepts, game system, general goals and overall play are concerned, it is very similar to D-Day 1961A, and, for that matter the following versions in 1965 and 1977. For an overview, the reader is referred to the descriptions of those versions.
There are rule differences that change detailed play and perhaps play balance. Significant changes from 1961A are: (a) One little-used Allied victory condition was dropped; (b) low combat odds calculation method is changed, (c) river combat rules are changed in several ways, including forbidding retreat across rivers(!); (d) fortress defense bonus is changed, (e) sea movement mechanics change, (f) some zone of control effects were altered, and (g) only one HQ is allowed per player (important because a typical tactic in DD61A and DD65 is use of German HQ units for paratroop defense). Some changes were simply to explicitly state rules that had been intended but omitted (e.g., allowing soak-offs at < 1:6 odds), but many omissions and key gaps in DD61A were not filled in DD61B (these largely relate to supply rules). The rule changes changes collectively make tactical play considerably different (a deployment that is good for one game version is probably not good for the other).
D-Day seemed to be a favorite in the early years of board wargaming, probably because of the appealing historical subject (this game came out only 18 years after the historical event; if kids playing this game didn’t remember the events, their parents certainly did) and the considerable variety in the course of play brought about by the many combinations of German initial deployments and Allied invasion area choices. Rule difficulties are all readily resolvable (which is not to say that all players will come to the same resolutions). Overall, it was an enjoyable game for its era and state of the art.
Description by E_T_Lee; source: personal observations and opinion.