It is an important decision which units you want to build in your cities. Production times are relatively long, so you need to plan early which units will be useful to you in 20 or 30 game turns.
Overview over the different unit types
Army
Armies can be built most quickly. Being land units, they can conquer cities for you. However, they move relatively slowly, and their combat strength is very low. It is usually more useful to build tanks than armies, but if you have just conquered a city in enemy territory, it maybe vital to build a unit fast.
Armies are the only units that can build roads.
Tanks have twice as many hit points than armies. This gives you the opportunity to repair damaged tanks (armies are immediately removed when they are hit). Tanks can also conquer cities, and tanks move slowly, too.
Aircraft cannot conquer cities, and their combat strength is quite low. Their main advantage is their high movement rate of five tiles per turn and their independence of the terrain. On the other hand, their movement range is limited: they can move at most 20 tiles before they pass one of your own cities for refuelling. If the 20th move of an aircraft does not end in one of your own cities, the unit will crash and be removed from the map. Aircraft are very useful for exploring the surroundings of your cities very fast.
As soon as you have fully explored and conquered your own islands, you will have to move armies and tanks to other islands (only land units may conquer cities!). In order to do that, you can build ferries for the transportation of your land units. Using ferries can also be useful if you want to move on a large continent: Moving two tiles per turn they are faster than land units (unless you've built roads). With two hit points, ferries are not very safe against attacks, and repairing a ferry will take quite long.
Gunboats can move almost as fast as aircraft. They move up to four tiles per turn, and their range is not limited to the surroundings of your own cities. With two hit points, they have the same combat strength than ferries. Gunboats are good for exploring the map, but some inland tiles will be out of their reach.
Frigates are a bit larger than gunboats. Their combat strength is significantly higher (four hit points), but they are a bit slower, moving only three tiles per turn. Frigates are useful in many ways: They can be used for exploring, but they can also hunt down enemy ferries (being faster than those) and thereby protect your islands from invasions.
Battleships are the strongest units in the game. With as much as seven hit points they can win several battles without being repaired. Damaged battleships can be required quite quickly in your own cities. Battleships are very good combat units, but their slow movement of only two tiles per turn will give some of your enemies the opportunity to delay or avoid encounters.
Moving three tiles per turn, submarines are good explorers. With only one hitpoint, they have only small chances to survive combat situations. Submarines will not appear on the screen of other players, so you can use them to explore enemy islands without being noticed (This is usually more important if you are playing with human opponents).
Mineboats take very long to build. With only one hit point and a low speed of only two tiles per turn they are easily destroyed by enemy units. Still, if you can manage to keep your mineboat for a while and place mines in the water, you'll get a good advantage over your opponents who don't know where the mines are put. A ship (including yours!) entering a tile with a mine will have a 50 % chance to loose one hit point.Back