After seeing a lot of contradictory information about mobilization, I did a fair amount of experimentation with it -- and found in the processs that I didn't really know as much as I thought I did about mobilization.
Here are the results:
Fundamentals of Mobilization Revealed
What is mobilization?
After the discovery of Nationalism, you may elect to mobilize your economy for war. During a war-time economy, in any city building a military unit (but not a military improvement more on this below), each tile being worked by a citizen that already produces at least one shield will produce an extra shield, substantially increasing production in that city.
Sounds great. What are the downsides?
During a war-time economy, your cities may only undertake building projects of military units or militaristic city improvements, with some limited exceptions (see below). Cities building non-militaristic units before the war-time mobilization may continue their non-military projects (without the shield bonus provided by mobilization), provided that, once such project is completed or is changed, the city will come under the same build restrictions as a city starting a project after the mobilization. Therefore, no new construction of temples, marketplaces, aqueducts, or a whole host of other city improvements is permitted after a mobilization. Also, during a war-time economy, each cultural improvement in each of your cities will generate only half of the cultural value it would normally produce. Finally, as noted more fully below, a war-time mobilization may not simply be abandoned by the player; a peace treaty must be signed with at least one AI civ (or an AI civ with whom you are at war must be destroyed) in order to return ones economy back to a peace-time.
How do I mobilize my economy for war?
Click on the bar labeled Mobilization in the Domestic Advisors window (it appears just below the Government bar in the upper right portion of the screen, below your science and happiness tax sliders).
Do I have to be at war to mobilize my economy, and how do I get back to a peace-time economy?
You are free to mobilize your economy at any time after you discover Nationalism -- you need not be at war. But you cannot freely return your economy to a peace-time mobilization at your whim. Once mobilized for war, only a peace treaty or the elimination of your opponent will allow you to return your economy to a peace-time role. If you are at war with several civilizations, a peace treaty with any of them, or the destruction of any one of them, will cause you to revert to a peace-time economy, even if still at war with other powers.
What constitutes a military unit or militaristic city improvement and therefore may be both (1) built, and (2) a shield-bonus-generating project, during a mobilization?
Well, if only it were that simple. There are actually two distinct categories of build projects during a mobilization: 1) units / improvements which may be built; and 2) units which may be built and will generate a shield bonus during their production.
The first category includes: (a) every unit with an attack / defense value or bombard value (ships, planes, artillery, missiles, and foot soldiers, including all UUs), (b) settlers, (c) workers, (d) scouts / explorers, (e) armies, (f) certain city improvements (see below), and (g) certain wonders (see below).
The second category, those building projects which generate the shield bonus, is more restrictive and is limited to those units with an A/D value or a bombard value, but specifically excluding: (a) naval and air transports (galley, caravel, galleon, transport, helicopter), and (b) armies. Although an aircraft carrier might be considered by some as primarily a transport, it will generate a shield bonus. No city improvement or wonder of any kind will generate a shield bonus, even if it is a permitted building project during a mobilization. And no production of workers, settlers, or scouts / explorers will generate a shield bonus.
What city improvements can I start during a mobilization (even if they dont generate a shield bonus)?
The following are all considered military improvements whose production may be started during a war-time mobilization: barracks, walls, SAM missile battery, coastal fortress, harbor, airport, and any of the spaceship parts.
And what wonders can I start during a mobilization (even if they dont generate a shield bonus)?
The wonders (great and small) which may be started during a war-time mobilization are: The Great Wall, Sun Tzus Art of War, Leonardos Workshop, Universal Suffrage, The United Nations, The Manhattan Project, The Pentagon, Strategic Missile Defense, Intelligence Agency, and Battlefield Medicine. Note that it is permissible to build the spaceship parts if you have already completed the Apollo Program small wonder, but the wonder itself may not be started during a war-time economy. Note also that although you may start the Military Academy small wonder during a war-time mobilization, you may not start the Heroic Epic small wonder.
SO . . . can you try and shorten this long-winded FAQ into a down & dirty summary?
Yes. During a war-time mobilization, your cities that are producing attackers or defenders generate extra shields, so much so that they basically mimic a golden age in terms of production. If not producing attackers and defenders, your cities can only produce a limited number of units / city improvements (unless the project began before the mobilization), and they enjoy no production bonuses. You can mobilize for war at any time (even during peace), but you need to enter a peace treaty or destroy an AI civ to end a war-time mobilization.
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