 Military units are used for combat against other players . Infantry are the cheapest unit type and all are land based , using weapons ranging from crossbows to early muskets to more advanced rifles . The heavier artillery classes also make use of ranged weapons , primarily cannon and mortars ; however , there is also artillery armed with grenades . Mounted troops are also present , and are armed with either hand weapons , such as swords , or ranged weapons , such as pistols . These units also have significant features , such as skirmishers which do bonus damage against infantry , and ranged cavalry does bonus damage against other cavalry . A new unit introduced in Age of Empires III is the explorer , which is chiefly responsible for scouting and gathering treasure but is also capable of building Trading Posts and has a special attack , used at the player 's command . This unit cannot be killed , but can be rendered unconscious , to be revived when friendly units are in range ; also , a ransom can be paid to have it reappear at the player 's town center . This ransom is credited to the player that disabled him , when applicable . Some shipment cards increase the explorer 's effectiveness in gameplay ; for example , providing it with " war dogs " can aid scouting and combat . In Age of Empires III , ships are available on most maps . Military ships makes use of cannon or flaming arrows , while some ships can collect resources or transport land units . 
