UEF is considered the ‘basic human’ faction of the game and has generally higher health –lower speed units in comparison to other factions, they focus on a more defensive play style, and you will find that the faction needs to reach a higher level tech to gain access to their unique units.
All reside in the T3 stage and reaching those higher levels gives you far more advantage over opponents in other factions. Combined with the T3 Bot Percival, quite possibly the strongest single land unit in the game, mass for mass with 9000 hp and 1600 damage per a single shot; often results in the UEF’s enemies being placed on a countdown timer, with 1v1’s reaching T3 often resulting in UEF victory if the opponent has not reached a large enough advantage. You also have the longest-ranged battleship, and some powerful T3 air tools if the game reaches that stage, but without Advanced Resource Allocation System (ARAS) upgrade on your ACU you could find yourself lacking the ability to rush as fast as other factions without keeping some of your old Generators around.
Hitting the T4 stage gives UEF the Fatboy, a mobile factory with 4 battleship-level cannons. Providing a lot of damage from a huge distance as the unit rains down shells from afar, but with little hp and only a shield to defend it makes the Fatboy very vulnerable without energy, Intel, or air cover.
But you need those three to win no matter the faction, so…
You also have the Mavor, the largest gun in the game with unlimited range and unlimited time to build if your eco is trash, and the Novax satellite. Which cannot be destroyed unless the enemy comes into your base and destroys its control station. But how one would manage to complete one of these weapons in a 1v1 game without losing from the mass/energy investment is beyond me.
The final T4 you own is the Atlantis, a giant sub that makes planes, it dies to its mass worth in regular subs and ground-firing battleships at it will cause major damage, so be careful where you use it.
However, all these units being higher tech does not mean you should play defensively until then.
While you are possibly slower than other factions, you still need that vital map control, reclaim, and mexes to win games, not only this, but you have the worst TMD. And the second worst T2 shield, so other factions have plenty of viable options to bust open your firebases. Keep fighting as you would with another faction, and make sure you cover potential raiding areas.
Anyway, into the somewhat detailed breakdown. This will probably be land focused with some comments to the other three branches if they are needed.
In the T1 stage, you have the Snoop, a little bikelike vehicle with 4 DPS and 29hp. That is your land scout, and you will be making these at almost any point in the game, this unit provides your hordes of tanks to see potential defences and units. They spot targets for your AA and artillery, making solitary PD almost 100% useless if you don’t try and wade through it.
You then have the Mech Marine. A LAB (Light Assault Bot) is the weakest unit stat-wise in your army, having low hp, 75, and reasonable dps (almost the same as t1 tanks) at 23. They build quickly and move fast, though, so they can be built and used to fight early-game on small maps. It's usually viable to raid with any LAB, of any faction (UEF, AEON, CYB) on maps that are 5x5 or 10x10km, but it is map-dependent. Common use includes sending a few of these out early to attempt to kill off engineers to hamper your enemy's start. Do not expect them to survive against t1 tanks, they will die in 2-3 shots without micro. All LABs can also enter transports and have the unique ability to fire while inside, creating a "Ghetto Gunship".
The vehicle that will be doing all the fighting for the UEF T1 stage is the Striker. It’s the most generic tank in the game, and it has slightly more hp than the other tanks, leading to it winning 1v1 fights, and the fire rate of the Striker makes it easy to dodge enemy tank shots, while still hitting your own as the turret can move fast enough to deal with your movement. However, the Aeon Aurora in numbers of >3 will easily win over your strikers, as they do again all other t1 land units due to their range and easy ability to move backwards without turning. They are slower than other t1 tanks, and if an Aeon opponent does not pay attention you can catch them. Aurora has such low hp that if you can get into range, and you are not heavily outnumbered when doing so, you will win easily. It's important to note that dodging from side to side with your entire force simply by clicking to the left and the right as they move will avoid many shots from Aurora as you engage/run away.
This doesn’t mean that a Striker can go 3v1 against Mantis or Thaams, as the numbers have to escalate for the hp bonus to stack up, being only a meagre 30/20 hp extra respectively, scout and anticipate enemy movements to block raids or force your way into expansions, your choice.
Sporting probably the most meaningless single-unit ability in the game, the Lobo is a higher damage, slower firing artillery unit with a ‘fragcam’ that gives the shells vision when they land for a brief second. It may be amusing to watch a PD die but you should probably be looking at something else by then. The Lobo is very good against stationary targets, as it does a large amount of damage with a single shot, and it's accurate. It's weak against moving ones due to the low rate of fire, as it is easy to dodge. Blocking units with strikers or building placements will allow lobos to hit more and deal large damage.
On a side note, the UEF bomber uses napalm and instead of dropping a single accurate bomb like Aeon or Seraphim bombers, it drops its load in a thick line so it's ideal for killing clusters but not as good for killing ACUs (they can dodge the bombs). Your frigate has jamming, meaning enemy frigates will sometimes shoot the fake blips instead of your boats.
(Also, build walls)
At this point, you would have used your ACU in combat and are possibly the best at doing what unupgraded commanders do, which is tank damage. The UEF acu has the highest base HP and is very versatile, allowing you to have very powerful combinations such as Gun + T2 + Shield, RAS + T3 + Shield, and even a Tml launcher that fires either regular missiles or nukes.
Your gun upgrade does double damage instead of shooting twice as fast, and this is especially good against Aurora, as it will 1 shoot them. It also won't overkill tanks like other gun upgrades do, as they will fire 1 more shot than is required to kill units due to the rate of fire, shooting an extra shot before the last shot destroys a unit. The gun is very effective vs t1/t2 armies, the range increase allowing overcharges and easy destruction of t1 units from a safe range. The kills from this give veterancy, which in turn allows more use of the ACU as a front-line unit. The T2 upgrade can act as an addition to this usage, the hp and regen it provides allow for a much tankier combat acu vs t1 and t2, with the bonus of build power for t1 buildings and the ability to make t2 (usually, pds and shields) The t2 upgrade on its own still provides hp and regen, and is inevitably essential in any game, for the hp, regen, and safety that extra brainpower grants. UEF t2 pd is strong against t1 units, as their 3 shots will hit clumps of enemies rather than just 1, usually killing multiple t1 tanks in single shots. A UEF player pushing can build these to augment his forces while in the field, but remember when and when not to use t2 pd - if you need dps near you, you want to build t1 pd. If you want to deny an area/long-range pushing/fire support, build t2 pd. It's important to note that point defence is not cost-efficient, and you still need an army. Obsidians and Ilshavoh can solo t1 pd easily.
Being able to get both the gun and T2 upgrades can help make your ACU a dangerous weapon in many open maps, and some may consider using the Shoulder drones or Shielding to add extra advantages.
When you hit Tech 2, you have three different direct-fire land units to choose from, the Pillar, which is a Striker with 5 times the hp, more range and DPS. It is a decent and effective mainline unit and is the cheapest regular tank at the T2 stage (100 less mass than a Cybran Rhino) offering you an affordable T2 unit to spam in very high numbers, use these units to your advantage.
Next is the Mongoose, a fast raiding bot with lower hp and higher range, allowing you to kite most t1. Similar to the Cybran Hoplite, it is a long-range bot used for kiting - avoid direct engagements with them and keep your distance - they are weak to bombing runs and also swarms of t1 tanks that get in too close, although a secondary grenade launcher can offer some saving aoe. These are not recommended for newer players due to the attention required to use them effectively, they require lots of APM and good radar coverage so try not to use many to start.
Riptides are the other unit, with a lower range and higher hp. It is your hover unit and its weapon gives almost no overkill, being a constant hail of bullets. It’s also more expensive than the two aforementioned units and isn’t common in most land-based games. It can be used as a raiding unit due to its speed but on land, its use is highly situational.
You have a generic flak gun called the Sky Boxer and a generic mobile missile launcher called the Flapjack, you also have a generic mobile shield called the Parashield which has similar equivalents in the other factions.
And then, towering above other T2 units is the Sparky. It's a field engineer and has more build power than the base engineer but can only build defences. [They have almost twice the build power of normal t2 engies and are very, very fast. Faster than most t2 tanks. They can make all point defences, shield generators, tml, tmd, and walls. They can be built from land, air or naval factories. It has jamming, radar, and defensive weapons, can hover, can reclaim, and can pull off entire PD creeps just as well as your ACU. Because you should always be trying to lay your hands on as much reclaim as possible, the Sparky gives a massive advantage and can trample raids with some micro. You can also reclaim enemy units while they are still alive for additional damage. Sparkies are also useful in drops where you build point defences in the enemy base.
Your Bulwark T2 shield boat is a powerful unit and confers a massive bubble around your boats, providing massive advantages in the water. The UEF does not have a T2 submarine, but instead has a torpedo boat. These are extremely effective against submarines, at the cost of being vulnerable to surface fire. They have one of the best torpedo defences in the game and are the perfect unit to build against submersible units.
Your gunship can lift single T1/2 units with a clamp, which can be used to drop engies or Pillars without having a transport.
Tech 3 is where a UEF player starts to get ahead. If you get it early, you can deal crippling damage to your enemy. The most important unit is the Percival mentioned earlier, 1600 damage means small numbers of this bot will straight up kill ACUs in a few hits, and large mobs will kill T4 units with low casualties. It’s good, use it.
To make up for the one thing Percival does not have (speed), you have the Titan. It’s a fast-raiding bot with a shield and two fast-firing guns. In comparison with the Loyalists, it’s garbage but Titans can manoeuvre and flank around to kill supporting units, engineers, or mexes. Use its speed, it’s all it has. If you have been spamming Pillars as we suggested, making the swap straight up to the far more effective Percival is a better option.
You have the Demolisher for a mobile artillery piece, and that is generic too, but T3 mobile arty rips through firebases and you will want to deploy these against static opponents. you also have the Spearhead if you prefer missiles over shells, they are extremely cheap and better at dealing with buildings, but useless against mobile units, unlike the Demolishers. You also have the Cougar, which has two miniguns to snipe out air units well; use it against strategic bombers and fighter-bombers. Against gunships, however, your mobile T2 flak is more efficient as its AOE damage can harm many gunships at once.
You also have the benefits mentioned at the start of the guide, and those are also immensely powerful. Creeping Ravagers is a solid move if you have the eco and do it before the enemy can respond with artillery. The Continental can drop six Percival at a time, doing so requires you to have T3 air; but if your enemy does not have considerable anti-air, you can land 9600 damage per volley wherever you choose, killing most ACUs in under 2 volleys. Percivals are faster than ACUs too, if you’re playing against UEF in T3, be careful.
Your T3 battleship is the best because of its range and your T3 gunships tank well. You also have the aforementioned Battlecruiser, which is extremely powerful against T2 and T1 naval and hover units. In combination with frigates and shield boats, the UEF T3 navy is the strongest in the game.
To rehash, UEF units are slower with more hp, they have good options on the land and you are allowed to focus on gaining high-tech levels to gain advantages. You have a good range of defensive buildings but don’t rely on them too much, and also, build walls.