Supreme Commander 2

Each mission has 1 or 2 hidden objectives. They are not listed by pressing but you receive "Objective completed" once you fulfilled the requirements. For a detailed list please check the corresponding Missions, too. Thanks to the GPNet forums for revealing this list.

UEF
Mission 1:
Survivor - Survive the First Wave of attackers without losing a single unit.

Select all units and park them near your factories. With your ACU build 3-4 Turrets at the north end of the factories and with the 2 Engineers build 3 Turrets in the south of your base, but keep in mind that you have to repair the turrets. Once they are finished you will receive the message upon completing this objective.

Mission 2:
Economic Opportunist - Build at least two Mass Extractors on enemies territory.

Build either a rather large group of Bombers or Gunships and destroy the marked Mass Extractors (secondary objective) and once they are gone and you secured the position send your ACU or Engineers to build two Extractors.

Mission 3:
Master of the Seas - Build an Atlantis II Experimental Aircraft Carrier.

You have to research the naval tree to unlock this unit and build it with either ACU or Engineer in the water. Once it is finished to fine.

Mission 4:
Brutal Conqueror - Defeat Coleman without the aid of the Fatboys.

Best done on Easy. You have to destroy the enemy ACU without conquering Bravo and Charlie Position. So build an army of 50-60 Bombers with upgrades and send them to the northeast and bomb the ACU to oblivion.

Mission 5:
Experimenter - Build at least four Experimental units

Since you are under a lot of pressure and the Fatboy is your best bet to hold your line, this will come automatically.

Mission 6:
Nuke King - Launch your first nuke.

You have to research the Nuke in the structure tree and after you've build it, order a nuke by holding and press and wait 2-3 mins. To launch the nuke select the nuke silo and confirm the target with .

None Shall Pass! - Prevent any enemy King Kriptors from crossing the main fortress bridge.

Since the KKs only advance after you destroyed the first of the three generators you can destroy them with 90+ upgraded bombers quite easily. Avoid fighting them the hard way or you will find yourself in some major trouble.

Illuminate
Mission 1:
Blockhead - Prevent the blockade from taking more than 25% damage.

Capture all turrets you find across the map and for the far remote ones, leave 1-2 Engineers to repair them while the Cybrans advance.

Mission 2:
Master Tactician - Complete the operation by constructing fewer than 30 mobile units.

Use your ACU and Engineers to build Point Defense Turrets. Surround your entire base with lots of turrets. Once you are safe build 8 Wilfindja and send them north. Save before you do this, as you have to destroy the 6 factories and a Colossus Bot afterwards.

Mission 3:
Agent Provocateur - Capture all of the Security Stations.

There are two islands one northwest and one southeast with a small base and the security stations. Once you destroy the shield and everything else some Terror Gunships will close in, which you need to destroy before capturing the stations.

Mission 4:
Experimental Fanatic - Have at least eight experimental units at the same time.

You need 8 experimental units in the field. So either you build 8 Colossus bots and overrun the bases or build something else which can be built faster.

Mission 5:
Supremest Commander - Reach the highest level of veterancy with your ACU.

Not as tough as you might think. Cover your base with Shields and upgrade the damage of your ACU. Park the ACU north east and wait until it reaches Rank 5.

Mission 6:
Note that you can only do one objective during the mission, so replay it afterwards.

Bot Lord - Complete the operation with an army made up entirely of Assault Bots.

You can't build any factory add-ons, Shields, Turrets nor any other attack unit other than the standard Assault Bots you unlock via Tech Tree. So build a lot of Land Factories (4-6) each supported by 3 Engineers and pump them out. Best done on Easy.

A Czar is Born - Build your first Darkenoid.

First you need to research the Darkenoid and then just build it.


Cybran
Mission 1:
Survival Expert - Survive Gauge's onslaught after the download completes.

Mission 2:
Master Thief - Capture a Rogue Engineer.

After you start the mission, send a Engineer to capture the rogue one which is building anti air turrets in the north of your starting point.

Great Escapist - Complete the operation without a unit being captured by the enemy.

You have to finish the mission without either a unit, building or turret captured.

Mission 3:
Cache and Carry - Collect all of the Technology Caches.

There are 5 Tech Caches placed on the different isles. One is on the isle south of the lab and a bit east of the structures there. The next is northwest of your starting point. The third is on the isle north of the lab and northeast of the structures. The fourth is hidden on the most northeastern isle and the last is south of the enemy base on the small isle.

Mission 4:
Sultan of Soul - Build at least four Soul Ripper Experimentals.

Research the Soul Ripper and the build four of them.

Mission 5:
Master of the Deep - Build a Kraken Experimental Submarine.

Research the Kraken and build it in the water.

Mission 6:
Research Savant - Complete all available research.

Just complete the mission with everything researched. To speed up the process build a large number of Research Facilities.

Master of Pawns - Win the operation without the aid of any Experimentals.

Instead of building Experimentals, build a massive air force of Geminis and aim for the enemy ACU. Note that even building any experimental building will void this objective. The message regarding completion of this objective comes after the Outro sequence.