I provide tips for how every unit should be built and used, and in what situations. I strongly recommend reading this section before diving into the mission guides.
Land Units
Infantry (1000G)
Infantry are the backbone of any battling army. You need them to capture cities, factories, airports, ports, and most importantly, the enemy HQ. From a battle perspective, their main purpose is to overwhelm the enemy with a lot of units. They're excellent cannon fodder, so if you're not building anything else because of low funds, build infantry. Infantry units have the lowest deployment cost. They have low firepower, but can capture cities, bases, airports, ports, and HQs, so they are critical to victory in numbers.
Infantry should be used to attack other infantry, mechs, transport units, and indirect units like artillery and rockets. Infantry will fight poorly against all other units. Infantry can also defeat low-HP vehicles and copters. In Fog of War situations, put infantry on a mountain and they will be as effective as a recon.
Mech (3000G)
Mechs are slower, more expensive infantry that can hold its own against most direct units like recons, tanks, and anti-air, while doing significant damage to indirect units like artillery and rockets. Mech units can capture cities, bases, airports, seaports, and HQs, traverse most terrain types, and have superior firepower compared to infantry.
Mechs should be used to attack mechs, recons, tanks, anti-air, artillery, and rockets. The bazooka can be used three times against those units and then you'll need to bring an APC to reload the bazooka, or have the mech reload at a city. Mechs can also attack infantry, but it's better to use infantry against other infantry due to the lower deployment cost of infantry. Mechs can run into trouble trying to get into range of an artillery or a rocket to attack it, but other units can be cannon fodder as your mech makes it over, or you can make use of a transport like an APC or transport copter.
In Fog of War situations, put a mech on a mountain and they will be as effective as a recon. Sami's mechs in particular are lethal, particularly when Sami has a CO power going, because of Sami's +1 movement on a CO power.
APC (5000G)
APCs can't attack, but don't discount their importance. First, APCs can transport infantry and mechs on land, which enhances the movement of both units in getting to a city, base, airport, seaport, or HQ to capture it at a much faster pace. And even if you don't use it for that purpose, APCs will refuel other units, particularly submarines, mechs, and indirect units that have a limited number of shots before they need to refuel. And if you're playing against the AI, the AI loves to target APCs, which can allow you to save more expensive units like medium tanks, rockets, air units, and sea units from being in the line of fire.
Recon (4000G)
Recons have a high movement range of 8 and vision of 5, which makes having a recon or two indispensable on Fog of War maps. Recons can do decent damage against infantry and mechs if they attack first, but its primary asset across all maps is their speed. Recons can slip past artillery and rocket ranges and attack them head on and do some damage. Avoid using them against tanks, medium tanks, anti-aircraft, or aircraft, because they won't stand much of a chance.
Tank (7000G)
Tanks are the bread and butter of a mechanized army. Tanks have good movement at a decent deployment cost of 7000G, and will smash infantry, mechs, recons, and indirect units like artillery and rockets. Most importantly, they do a bit more damage and win the head-to-head against the slightly more expensive anti-aircraft. Do not use them against battle copters or medium tanks, and watch out for mechs that may be within range, because a mech that strikes a tank first is going to be a problem for a tank.
Air Units
Transport Copter (5,000G)
Transport copters are APCs that can fly over all types of terrain, but without their fueling abilities. Use them to transport infantry and mechs across seas and mountains so that they get to their destinations quickly. Transport copters are the fastest way to move an infantry or mech to a neutral property or HQ, but keep in mind that like APCs, the AI knows this and will often target your transport copters first. Alternatively, because of this, you can also use transport copters to lure enemy units so they do not attack another expensive target you have.
Battle Copter (9,000G)
Battle copters are the tanks of the sky. They can be used to attack many of the same direct units that a tank can, other than anti-aircraft, but have much more movement flexibility over all terrain types. They are useful for escorting early transport copters, and because of their movement range, battle copters are more effective at striking indirects as long as there is not an anti-air nearby ready to take them down. In battlefields with heavy air and sea presence, battle copters are excellent early-to-mid game units. Watch out for fighters, anti-aircraft, and missiles.
Fighter (20,000G)
Fighters are the medium tanks of the sky. They have a high deployment cost, but if you want control of the air to keep your battle copters and bombers safe, fighters are essential. Fighters will destroy all other aircraft, but as with any other air unit, they must be careful around enemy fighters, anti-aircraft, and missiles. Do not build fighters unless you know your opponent will build planes, because fighters can only attack air units.
Bomber (22,000G)
Bombers are the all-powerful air assault unit. Bombers can take out nearly any land or sea unit, except submerged submarines, if they attack first, and they have a strong movement range of 7 to fly through enemy lines. Bombers are expensive, so protect them carefully from fighters, anti-air, and missiles. Generally, keep them out of enemy fighter range or weaken enemy fighters before moving bombers in. Bombers can still damage anti-air and destroy missiles on first strike, so make sure the bomber attacks first.
Stealth (24,000G)
Stealth fighters are advanced aircraft that can cloak themselves, becoming invisible to most enemy units unless detected nearby. While cloaked, they can slip past defenses and strike vulnerable targets with surprise attacks.
Their greatest weakness is fuel consumption. Cloaking drains fuel rapidly, and a Stealth that runs out of fuel crashes immediately. Because of this, Stealths require careful planning and constant awareness of airport access. They are best used for surgical strikes, not prolonged hidden patrols.
Black Bomb (25,000G)
Black Bombs are flying suicide weapons designed for maximum area destruction. They explode on command, dealing massive splash damage over a wide radius, often crippling entire enemy formations in one strike.
Because they are consumed when detonated, Black Bombs are high-risk, high-reward units. They are most effective when enemy forces are tightly clustered, such as around factories, chokepoints, or defensive lines. A well-placed Black Bomb can instantly swing a battle, but poor timing wastes enormous value.
Sea Units
Black Boat (7,500G)
Black Boats are hybrid naval support transports. Like Landers, they carry two infantry-class units, but they also repair and resupply adjacent naval and land units. This makes them one of the most flexible support ships in the game.
They are fragile and cannot fight effectively, so keep them protected behind your frontline. Black Boats are especially useful in missions with long naval routes, island invasions, or extended campaigns where APC-style resupply at sea is critical.
Lander (12,000G)
Landers are the main sea transport unit, and much more expensive than APCs and transport copters. Like transport copters, landers cannot refuel other units. However, landers can transport two units at a time, not just one. And furthermore, landers can transport any two land units, not just infantry and mechs. This means that landers have the versatility to move tanks, medium tanks, artillery, and rockets across sea-driven maps and deploy them into battle. Landers are not particularly vulnerable to direct land units, but they can still be taken down easily by indirect units like artillery, rockets, and battleships, as well as submarines and bombers.
Cruiser (18,000G)
The cruiser is the more expensive seafaring version of the anti-air. On land maps, build anti-airs instead, but at sea there is nothing better for taking out air units and submarines. Cruisers are highly effective against fighters and battle copters if they can get into range. Cruisers are also extremely effective against submarines, provided they can locate where the diving submarine is. Watch out for battleships, which can destroy cruisers from long range with their 2-6 firing range.
Submarine (20,000G)
Submarines are the medium tanks of the sea. They are expensive, but their ability to dive makes them indispensable. Diving allows submarines to approach battleships covertly and destroy them, and also lets them ambush enemy submarines and loaded landers. Diving uses fuel quickly, so be sure to refuel every several turns with an APC or by resting in a port. Submerged submarines are harder to detect, but are still vulnerable to bombers, battleships, and indirect attacks. Always beware of cruisers, which are specifically designed to sink submarines.
Battleship (28,000G)
The battleship is the second most expensive unit in the game, and rightfully so. With its 2-6 firing range and few counters, it can destroy most sea and land units without being directly threatened at all. Battleships outrange even rockets and missiles, and no direct land unit, even medium tanks, can do much damage to them. However, they are still vulnerable to bombers and submarines. A cruiser escort is often useful in defending against air attacks. While battleships have incredible range, be aware of artillery and rockets that may get in range first, or else you may find yourself yelling, "You sunk my battleship!"
Carrier (30,000G)
Carriers are anti-air warships that combine naval durability with aircraft support. They can carry two air units and automatically attack enemy aircraft that come into range, making them powerful anti-air control ships on water-heavy maps.
Their offensive role against sea and land targets is limited compared to battleships, so carriers should be used as fleet support rather than primary attack ships. They are strongest when protecting bombers, fighters, and naval formations from enemy air harassment.