Faction Tech Trees feature

UNSC

HQ-Militia, Naval Pioneer (builder), Spartan 2
upgrade
HQ 1
HQ 2

Barracks
Marine Group
ODST Stealth Group-HQ1
ODST Fireteam-HQ1
ODST Bullfrogs-HQ1
Flamer
Heavy Weapons Squad
Anti-Tank Squad
Pathfinder team (sniper)
Spartan 3 team-HQ2
Sargent Johnson

Armory
upgrades
increase number of heavy weapons in marine squads

Vehicle Building
Warthog
Rocket Warthog
Transport
Artillery
Grizzly Heavy Tank-HQ2
Scorpion-HQ1
Mongoose
Elephant-HQ2, Relic

upgrades
increase scorpion turret speed
increase fragmentation damage of scorpion shells

Orbital Relay
ODST Fireteam
ODST Bullfrogs

Covenant

HQ-Engineer, Grunt lance, Prophet, Arbitor
upgrade
HQ 1
HQ 2

Barracks
Grunt lance
Grunt pack
Elite Lance
Jackal snipers
Jackal Shield Squad
Brute Squad
Stealth elite
Grunt gunner squad
Brute chieftain

Elite Barracks-HQ1
Skirmishers
Suicide Grunt lance
Spec Ops lance
Hunters
Elite Jetpack
Veteran elite lance-HQ2
Elite Honor Guard-HQ2
Brute Jetpack-HQ2
Brute Guard-HQ2
Zealot

Armory
increase elite health regeneration

Vehicle Building
Wraith
ghost
Revenant
shadow
Spectre
Chopper
Scarab-HQ 2, Relic

Sentinels
HQ-Monitor, Constructor
upgrade
HQ 1
HQ 2-Unlock Prometheans

Barracks
Minor Sentinel Squad
Gold Sentinel Squad
Super Sentinel Squad

Sniper Crawler-HQ2
Alpha Crawler-HQ2
Crawler-HQ2
Knight
Knight Lancer-HQ2
Knight Battlewagon-HQ2
Knight Commander-HQ2
Watcher-HQ2

Armory
increase health of minor sentinel squads

Vehicle Building-HQ1
Enforcer
Strato Sentinel-HQ2, Relic
artillery unit

Rebels

HQ
upgrade
HQ 1
HQ 2

Barracks

Armory

Vehicle Building