The Allies Nations are a well balanced force armed with their Special Forces, along with their Mightiest Air Force in the world. Their Structures build in the Conyard unlike the Soviets and their Spies can infiltrate Buildings and Bribe the most powerful units to your side. The allies however have an inferior navy that will require air Support against heavier enemies.
Allies vs Empire
A strength of the Allied Nations is clearly their air superiority with their Mightiest Air Force. One strategy is Vindicator rush. With the ability to build these aircraft very early in the game, rushing to build an airbase as soon as possible and blitzkrieg-ing your enemies is a sure recipe for an early victory. This is really a base-killer when facing the Empire as their early anti-air defenses are weak at best. This strategy is not as useful against the Soviets. Ensure you don't fully neglect land defenses because you never want to leave your base fully undefended. Also make sure your Empire opponents haven't snuck a Nanocore to the sea where he starts building a secret deadly versatile navy base that will grow to challenge and haunt you in the future.
One more thing to be aware of is that the Empire will attack your Prospectors with the Jet Tengu and its transforming features.
Also, If playing on a large map or with the enemy a great distance away, sending Century Bombers filled with javelins and some Peacekeepers is a favorable tactic. Order the Century Bombers to attack power stuctures to shut down defensive structures or the defense structures themselves so the Javilins and Peacekeepers will land and finish them off. 2 or 3 Airbases with 8 or 12 Centuries respectively should destroy or cripple them. Once the Infantry is deployed send the Century Bombers back to reload, rearm, and repair while loading them with more troops. Make sure the Solders inside the enemy base are in Attack Position so them don't just stand around to be killed. This works pretty well against Soviets too but The Empire of the Rising Sun will regret challenging The Allies.
When facing The Empire of The Rising Sun always remember to attack from the Air with your Mightiest Air Force and stay away from Naval Battles, the Empire of the Rising sun always excels at, since they do have a Superior Navy at their disposal. The Empire is weak against Air attacks. Century Bombers and Vindicators are very effective against them. However the Allied Nations do have an outstanding navy, otherwise weak. Allies also have the best Infantry units back Javelins and Peacekeepers with your tanks. If you can't avoid a Naval struggle try giving your Navy Air support. Cryocopters are very useful at sea vs Japan.
Allies vs Soviets
The Soviet advantage lies with their Powerful Army in the World, beware of the Terror Drone and the Sickle. The Terror Drone has the ability to cripple your economy for a measly 500 credits, by disabling or destroying your Prospectors. The key to countering this is walling in the path between your refineries and their respective ore nodes. Sickles can be devastating to your infantry due to their machine guns and the Flea Jump. If you are intending to use infantry, never bunch them up and use the Scatter (X) key when necessary.
It must be noted that air sorties with Vindicators are not an efficient way to deal early-game strikes against a Soviet opponent due to the early availability of Flak Troopers and Bullfrogs.
One strategy that is effective is to produce 2 Multigunner IFVs and put an engineer into each of them. These vehicles then become "mobile repair units". Always produce at least 2, not just one, as they can then repair each other. 5 Guardian Tanks, 2 Engineers-Multi-Gunners, 3 Rocket Troops into a Multi-Gunner. This group of 10 can be used to rush an enemy base. The Guardian Tanks will form up front, and take the hits while the repair carts will keep repairing them.
One thing to be aware of is that the Soviets will use V4 Rocket Launchers if you dare to try to stop their Apocalypse Tank assaults and their Kirovs and Magnetic Satellites will make deploying troops difficult.
The Soviets will always go for their Tanks backed by their infantry against you. It is their greatest strength in the Soviet Red Army. So use your Air Force attacks from the skies to give your own ground forces some help. Also use Infantry against The U.S.S.R. as it is the arguably the weakest of the Three. When at sea, The Red Bear has been known to reform the slow moving Dreadnoughts, and if anything beware of Akula Subs, since they are a threat to most of your naval forces and Aircraft Carriers and Stingrays are also dangerous as well. Soviets have a very slow fleet, mainly the Akulas and Dreadnoughts are added with heavy armor and firepower as their main part of their navy, Air Force support maybe agood thing or otherwise. Don't forget to make use of Top Secret Protocols to slow down their MASSIVE ARMY( of tanks, infantry and sickle) Assaults( all together).
Allies vs Both
A highly efficient way to apply pressure on an opponent early in the game is to load a Riptide ACV with 5 Javelin Troopers, or two such Riptides if your economy allows it. The Riptide can handle a few infantry, while the Javelins can take out buildings and vehicles (remember to watch out for Sickles if facing a Soviet enemy!). Focus on production structures and Ore Refineries. Coupled with 2 or more Multigunner IFVs (possibly with Peacekeepers inside), this force may be enough to cripple the opponent for the remainder of the game. Don't forget to replenish your forces, as necessary.
If the initial strike fails, assess the impact of your attack. If your opponent will take some time to recover, try again. Otherwise, quickly reach Heightened Clearance and use Guardian Tanks in combination with a similar force mentioned above.
As mentioned before, the Allies possess a well balanced force with some exceptional examples. The Peacekeeper is arguably the best "grunt" unit of the three factions, the Hydrofoil is undeniably the best ground-to-air unit, with the added bonus of the weapon jammer. The Mirage Tank, though the weakest Tier 3 tank in the game, is the cheapest, and the easiest to conceal.
Engineers in Multigunner IFV Strategy 1: Have a few Engineers in your Multigunner IFV's so they can repair the vehicles as you attack. So the typical strategy is some Guardian Tanks, some IFV's with Javelins in it, and some IFV's with Engineers in it. Also have some Javelins with you. Set them to destroy enemy units only, and not buildings. Once you are next an enemy building, have the engineer jump out and capture that building. Engineers have no protection, can't defend themselves, and walk slowly. In this way, they can do double duty. They repair your vehicles when you have the engineers in IFV's, are transported more safely, and with this strategy, you can overrun a small base quickly. When your engineers are gone, have the extra Javelins jump into the IFV's and take over. One of the best buildings to capture are the Super Reactors, as they almost certainly will make the Russians go low power and give you a lot of power at the same time.
Engineers in Multigunner IFV Strategy 2: You can also use Engineers+IFV's to quickly repair damaged buildings. When your partner is attacking, you can send a few to help them out.
Inchworm Javelin Strategy: If you are in a heavily citied area, then you can build a lot of Javelins and put them into multiple buildings. Fortify 4~5 buildings close to each other. This will help them cover each other. Once the threats have been neutralized, eject the Javelins who are furthest away, out of the building and move them to the next building. Slowly inch your way up to the enemy's base perimeter. Use the Javelins in buildings to form a blockade. Also, if you are playing solo and your partner is the computer, consider putting a few Javelins into buildings by their base, because they normally don't.
Airbase Swap: You can "move" your airbase closer to your enemies so your Vindicators can bomb more frequently. You can do this by building new "empty" airbases closer to the enemy, have your vindicators attack. When the vindicators are in mid-air, SELL your old airbases. The vindicators will be smart enough to fly to the new airbases from now on. This not only increases the frequency with which you can attack the enemy, this also shortens flight time, so you are less vulnerable from being shot down.
Try rushing the Allies with Guardian Tanks. If it fails another strategy recommended on fighting the Allies is build Guardian Tanks in large numbers to overwhelm the enemy and have one Guardian Tank use its special ability to pinpoint and weaken enemies one at a time while the other tanks move in for the kill.
If your economy allows and enemy is held at bay try filling Century Bombers with Javelins. Have the Centuries attack enemy buildings. Then let the Infantry paradrop into the enemy base. About 6-8 Century Bombers filled with Javelins should do the trick. Or have Riptides filled with Javelins, use surveillance sweep to use the Chronosphere to attack them from within their base by having the Javilins exit the Riptides from inside the enemy base. Or you could combined both tactics to be even move creative.
Top Secret Protocols
The Allies have arguably the Best top Secret Protocols of the three factions. Utilizing them well is crucial.
The surgical strike works great on units, but poorly on structures. If the computer repairs its' structures, or against a human opponent, don't waste the surgical strike on a building unless it's already hanging by a thread. It is much more useful taking out an anti-air structure or heavy tank.
The time bomb cannot be placed directly on top of a structure or unit, unlike air strikes or satellite blasts. It is a chronosphere-transported unit itself, and must be placed in the space between buildings and units. It is also vulnerable to being targeted and destroyed by enemy units, so beware of placing it beside an offensive force run by the computer. A human opponent may not react in time to attack with their units, but the computer is pretty good at it.
The Chrono Chasm is both an offensive and defensive power. On one hand, it can be used to stall an attacking force if timed and placed correctly (though, the Cryoshot is more effective for this as you can destroy the frozen units easily). It can also be used to disable your own structures in the most dire emergencies. On the other hand, it can be used to stop the countdown on enemy superweapons, disable closely grouped power plants or a Super Reactor, or to phase out any defensive structures preventing you from disrupting your opponents economy.
The Allies have very versatile special abilities that can turn the tide of battle. The Bribe ability is an ability that makes even the biggest heavy units turn to the side of the Allies. This ability cost too much money however. The RTB order helps Apollos and Vindicators retreat to an Airbase quicker, and the Blackout missile disables non-infantry units in a great radius.
The Allies' Targeting Laser makes an enemy take more damage from your units, and they have one of the most useful abilities called the Shrink Beam which cause enemies to become easier to crush with Guardian Tanks.
The Century Bomber is one of the most powerful air units in the game. However, their bombs are inaccurate, and they tend to release bombs too early or too late. When using Century Bombers, issue a MOVE order to your target (or right next to your target). Once they are directly overhead, order them to attack the target (). This way, fewer bombs are wasted and more damage is done, especially to larger targets. A construction yard can be destroyed with ease in a single raid of four Centuries in this manner.
Also if you fill 8 century bomber with javelins to easily destroy a base(possibly escorted with apollos).
The Chronosphere can be used as a directly offensive weapon - you can use it to destroy enemy land units by teleporting them into the water, or naval units by teleporting them onto land. Amphibious can be destroyed by teleporting them into buildings.