Naval units are divided into several varieties:
Merchant marine units are generally civilian units. There are three types of ships: transport barges, merchant ships, and fishing vessels. Transport barges are formed whenever a land-based unit enters water; merchant ships are the maritime version of the trade caravan, and fishing vessels are boats which can collect resources from fish and whale resource patches.
Light ships are known for their speed, but have minimal armour and armament. They are the first naval unit to be accessed, and are available from the Dark Age.
The Dromond, an oared vessel is the first combat ship people access, and it appears in the Dark Age. It is upgraded to a barque, another oared vessel, in the Castle Age and is upgraded to a frigate in the Imperial Era.
Brigantines are a super light ship, and are available only to those who have Legalism researched and have access to the sloop at their dockyard. The Brigantine is substantially superior to other light ships as regards to hitpoints, speed, and rate of fire.
- Asian factions do not build sloops and brigantines, but instead construct swooper ships and covered swoopers. These units are the equivalents of the same.
- Factions under Muslim influence have access to a Fusta, a light galley class available in the Castle Age. While the Fusta is not as strong as more advanced ships later on, it distinguishes itself with its lightning-quick attacks and cheap cost.
Dromond  => Barque  => War Galley/Swooper  => Brigantine/Covered Swooper (with Legalism)
Heavy ships are buliker and slower ships, but they are endowed with better hitpoints, armour and firepower with respect to light ships. Unlike the light ship class, the heavy ship class is accessible only from the Castle Age, and the super heavy ship is accessible only by having Absolutism researched.
- The artillery on board heavy ships are inferior to that used by land artillery well until gunpowder becomes available.
- Carracks have substantially better armour and hitpoints, and a higher cost in construction compared to cogs. However, their rate of fire means that in ship-to-ship combat, they are second to none.
- Galleys are marginally only sturdier than cogs, but are classified with a slower-firing but further-reaching and harder-hitting projectile attack. Over time, however, galleys and cogs deal the same damage in a single minute.
Most factions do not get heavy ships until the Castle Age, however factions with Viking influence (England, Norse, Russians and Scots) however have access to the longship, a powerful warship which while weaker than roundships, has a range and strength approximate to the Roundship.
Roundship  => War cog  => Carrack and Lanternas
- Not everyone can build the same units. China and Japan don't build the same units as the Europeans do, but instead build a different line of ships. These ships all have large costs in wood, but minimal metal costs. The Asian factions, aside from Mongolia, thus will have problems similar to those of Russia, but it will be said that Japan is the best Asian faction for naval warfare, since it can conserve metal from forts and towers for ploughing into heavy ships.
- The carrack is available only to England, France, Spain, Burgundy, the Holy Roman Empire, the Norse, and Scotland.
- Portugal receives two unique heavy naval units, the nau, and the São Gabriel-class carrack. Their spooky black paint jobs and intimidating size (the nau is a smaller version of the vanilla carrack, but dwarfs the cog), these units are not to be messed with, although fire ships will do a number on them.
Progression: Siege barge  => Basilisk galley (with Centralisation) 
This category has the following 4 subcategories, out of 4 total.