Men of War: Vietnam is "being made in conjunction with Assault Squad, but is being developed by the same studio who made [Men of War] Red Tide (not DigitalMindSoft)," reads the Strategy Informer report noticed by BluesNews.
The site describes Vietnam as the third expansion in the series. The first two, Red Tide and Assault Squad, are standalone efforts that 1C bills as both expansion and sequels.
More details, including a release date, are expected alongside 1C's formal announcement. or a taste of the strategy series, hit up FileShack for demos of both Men of War and its first standalone expansion-sequel Men of War: Red Tide.