Source: http://world-of-ru.livejournal.com/3291114.html
What is the Stronghold mode?
New mode for clan players, available within the game and not tied to the Clanwars. A clan has a virtual base with buildings, road leading to it and additional constructs. Can be created by the commander of the clan free of charge, whenever he wishes, but the clan has to have at least 20 players.
The clan can develop its “stronghold”, construct buildings on it in order to access various economical bonuses, that can be activated for limited time. For example, increase of creditmaking of vehicles in the game, or increase the crew training speed – everything depends on stronghold development strategy. In the future, new features will be added to this mode, such as upon reaching a certain level of the stronghold, players will be able to attack enemy strongholds and defend theirs. During such battles, there will be unique features such as air support (bomber raid), artillery fire mission, minefields and others.