The Supply Port is a type of port in The Peninsular Campaign.
Description[]
A supply port improves the flow of goods and supplies into a region. It also allows some smaller ships to be constructed.
Moving military supplies by land is difficult and quite expensive; most roads are simply terrible! Anything that has to be moved more than a few miles goes by water whenever possible. A supply port lets a nation moves [sic] goods to where they are needed with a fair degree of efficiency. Military supplies go out, and goods from trading posts arrive from across the world.
During the 19th century, the British had the most powerful navy in the world as a virtuous circle of sea trade funded its existence, and a strong navy allowed even more trade. The new "industrial revolution" meant that manufactured goods were there to be traded across the world. Trade was important because it allowed Britain to finance wars as well as fight them. Allies could be supported with gold rather than men in the field. This was what prompted Bonaparte's Continental System of blockading British trade. It didn't work terribly well, but Napoleon knew that the way to beat Britain was to starve the country of money.
General Information[]
While they look identical to the trading port line of buildings in Napoleon: Total War, the supply port line of buildings differ in several characteristics. From an economic standpoint, they do not generate any wealth directly; indeed, if the player doesn't have a significant trade fleet stationed at trade nodes, there is little benefit to building them for money. The other substantial difference is that the supply port line of buildings increase the number of land units that may be recruited from a region, and that the higher levels also significantly reduce land unit costs. This makes regions with supply ports excellent recruitment centers in The Peninsular Campaign.
In The Peninsular Campaign, wealth generated from taxation is very low, with most regions having next to no region wealth initially. Income brought in from trade, however, can be very large, and can indeed constitute a majority of income, especially early on in the campaign. Supply ports help facilitate this income in two ways: by constructing trade ships and by increasing the amount of money generated by each trade ship.