Monitor

The Monitor is the "Battleship" of Age of Empires III. It has a mortar fixed in the front for bombarding beaches or fortifications, but is weak against other ships and anti-ship units. However, it has a long range ability, which allows it to fire a single shell from an extremely long distance, making it useful in a fire support role. Monitors are trained from the dock and can also be upgraded to an Imperial Monitor. They are able to be trained and upgraded in the Imperial Age. It is generally considered better than the Ironclad for long-range attacks.

Unction and Monitors
Due to the sizeable bonuses of the Unction aura for the Spanish, they are the only civilization capable of turning a monitor into an effective, although makeshift fixed gun on any map with a puddle of water large enough to hold it.

The high age requirements for the maximum damage potential makes this only realistically an option for the Spanish during Treaty games, or fights against A.I. opponents.