This achievement will likely come naturally over the number of online matches you play during your time on Halo Wars 2, but it can be done rather quickly in a solo Skirmish match against the AI on Easy. If you prefer to knock this out quickly, head into the Skirmish lobby and make these setting changes:
+ Gametype: Deathmatch
+ Starting Supply: 9999
+ Starting Power: 9999
+ Fog of War: OFF
Now make sure to set the AI's difficulty to Easy and choose a UNSC Leader. Take note that each UNSC Leader has an exclusive Unit to build, so you will have to redo this twice more to build those two Units at a later time.
When the match starts, begin building a few turrets to act as a proper defense (just in case the enemy attacks you), and then construct and upgrade one Generator and one Supply Pad for additional Supplies and Power. Next, upgrade your Base (the main building) to a Command Center for 1,000 Power (this unlocks Tier 2 Units). Once that is done, upgrade the Command Center to a Headquarters for another 1,500 Power (this unlocks Tier 3 Units).
You'll then want to construct one of each building: Airpad, Armory, Barracks, Garage. After these have been built, begin constructing one of each Unit from each. You can refer below for a quick checklist of what needs to be constructed for this achievement.
- Condor Gunship
- Douglas-042 (exclusive to Anders)
- Alice-130 (exclusive to Isabel)
- Jerome-092 (exclusive to Captain Cutter)
- Protector Sentinel (exclusive to Anders; 2 Leader Points needed - 1 to unlock, 1 to purchase, then you can construct at the HQ)
Once you have constructed all 18 Units, this achievement will unlock.