Basically, new versions contain less bugs, new units, balancing updates and so on. You should never play an older version than the latest version released here.

Version 21:
- Shields absorb any bullet targeting allies
- Shield modules deactivate properly
- Optimized performance for units with multiple weapons
- Very strong units are no longer removed when a player leaves
- Submerged units can no longer be repaired
- Fixed a bug regarding starting positions
- Fixed some crash risks
- Changed Light Assault Bot (T1) model
- Added Platform Areas (T2)
- Added Flame Thrower Recruits (T1)

Version 20:
- New Map: Sludge (3 players)
- Added Fortified Fraction Transmitter (T4): Empiron
- Added ACU Modules
- Added some effects
- Added "-info [x]" to receive information about the unit type named x
- Added single player command "-fps x" to change the physics fps
- Added simple no rush territory limitation
- Scaled damage, hitpoints and energy down
- All storages now affect mass and energy equally
- Automated shield activation
- Changed some attacks
- Fixed a storage bug
- Fixed some visual bugs
- Optimized some scripts

Version 19:
- Added Hydrocarbon Power Plant (T2)
- Added different prebuilt bases
- Changed some unit attacks
- Moved Heavy Artillery Installation (T3) to (T4)
- Moved Strategic Missile Defense (T4) to (T3)
- Improved Point Defense (T2)
- Improved "-debug", so it may also fix the resource bug
- Visible units no longer seem to be invisible sometimes
- Transported units are no longer harmed during an attack
- Fixed a burning trees bug
- Fixed a missile interception bug
- Fixed a texttag bug when captured units die
- Fixed a critical map border bug
- Fixed a construction bug with assisting workers
- Fixed a collision bug
- Fixed some victory bugs

Version 18:
- Ians Cross and Vya-3 now support 8 players
- Improved performance
- Fixed resource stats
- Fixed some minor bugs

Version 17:
- Added the possibility to enter part of names as arguments for commands
- Added -nap x for no attack pacts
- Added -cede x to give units to other players
- Added -create n x to create units in singleplayer (replay-incompatible)
- Added 111 hp to units with very much hp to reduce the length
- Added Destroy for the controller
- Added bullet shadows
- Added passive abilities to indicate missile/torpedo defenses
- Changed 0-0 attack damage to damage per second
- Changed Shield Generator (T2) buildtime to 36 seconds
- Changed AA Flak Artillery (T2) attack
- Changed some effects
- Changed air turn animation
- Changed unit limit to max. 1000 in total, max. 300 per player
- Changed capture, speed can vary and multiple units can work together
- Increased Tactical Missile Launcher (T2) missile build time
- Increased Point Defense (T1-T2) bullet Z
- Fixed missile and torpedo defense delay
- Fixed repair time for different tech-levels
- Fixed Phantom income
- Fixed storage for units in transport
- Fixed Fatboy (T4) texture on invisiblity
- Fixed CZAR (T4) texture
- Fixed a critical auto-production bug
- Fixed a shield regeneration bug
- Fixed a shared control bug
- Fixed some AI bugs

Version 16:
- Added Torpedo Launcher (T2)
- Added Tactical Missile Launcher (T2)
- Added Submarine Hunter (T2)
- Added Stealth Field Generator (T2)
- Added Heavy Tank (T3)
- Added Heavy Artillery Installation (T3)
- Added Defense Frames (T1 + T2)
- Added a cooldown to the Strategic Missile Launcher (T4)
- Added hotkeys for experimental units
- Added lightning attacks
- Added unit nicknames
- Added damage per second to -info
- Added 2x Defense Frame (T1) to prebuilt base
- Added the possibility to disable artillery
- Added minimap signals to nuclear missile targets
- Added energy costs to Artillery Installation (T2)
- Added food cost for some buildings
- Added Annihilation mode
- Added non-leaver-ai mode, where all mobile units are removed
- Added an Economy Display mode, which shows the income and dps against specific unit types of all selected units
- Added automatical division of unspent resources
- Changed resource board description
- Changed some effects
- Changed Air Superiority Fighter (T3) attack
- Changed AA Turret (T1) and Mobile Anti-Air Gun (T1) attacks
- Changed AA Turret (T1) and AA Flak Artillery (T2) models
- Changed range circles to be displayed under the terrain
- Changed Strategic Missile Submarine (T3) to non-aiming
- Changed Artillery Installation (T3) to (T2)
- Changed Mavor (T4) to Salvation (T4) with a split-shot-attack
- Changed Cruiser (T2) to a stronger anti-air unit, but removed its missile launcher
- Changed ally resource trading per click
- Changed secondary weapon targeting so they will keep their targets when moving the unit
- Changed the AI to a more defensive strategy
- Changed game mode selection menu
- Changed veterancy bonus to be displayed as hitpoints
- Changed range display to fade in and out
- Reduced Storage (T1) mass costs
- Reduced death damage by 50%
- Reduced ACU repair time
- Reduced delay
- Increased Torpedo Boat (T2) range
- Increased Mobile AA SAM Launcher (T3) damage
- Increased Mass Extractor upgrade time
- Weakened Mobile AA Flak Artillery (T2)
- Weakened Heavy Gunship (T3)
- Removed visible area around an attacker
- Removed auto-unally when attacking
- Improved ASsist when building structures
- Hydrocarbon and mass spots are now unselectable
- Artillery no longer fires when it is not provided with energy
- Slowed down tactical missiles
- Fixed a bug when repairing allied units
- Fixed Hydrocarbon Power Plant (T1) building restriction
- Fixed a high-speed-projectile collision bug
- Fixed an aiming rocket starting direction bug
- Fixed Fatboy (T4) Hitpoints
- Fixed some hotkeys
- Fixed -info

Version 13:
- Added Hydrocarbon Power Plant (T1)
- Added Mobile Bomb (T2)
- Added Mobile AA SAM Launcher (T3)
- Added Missile Carrier (T3)
- Added Land Raid Support (T3)
- Added lift force to projectiles
- Added -debug to fix a resource and damage bug (may already be fixed)
- Added -norush x for host
- Changed Mobile Light Artillery (T1) attack
- Changed Air Superiority Fighter (T3) attack
- Leavers will always be controlled by the ai
- Improved Artillery Installation (T3)
- Improved collision detection
- Improved projectile movement
- Improved missile defense management
- Improved range display, now only affects selected units and has a faster refresh rate
- Increased anti air precision
- Increased death damage delay
- Increased projectile limit
- Enabled resource trading
- Rebalanced Cruiser (T2)
- Reduced CZAR (T4) size
- Reduced unit turn rates
- Fixed a leaver ai bug
- Fixed some tooltips
- Fixed some other bugs

Version 12:
- Added -info command
- Added Burial Mounds map with volcano
- Added ai replacement for leavers without allies
- Added a nuke warn signal
- Improved performance and safety
- Improved credits
- Tweaked some rocket flight pathes
- Rebalanced ships
- Increased mana capacity of missile launchers
- Increased commander income by 100%
- Fixed an AI bug
- Fixed a defeated player vision bug
- Fixed some other bugs

Version 10:
- Improved graphics
- Improved system safety
- Improved team placements
- Improved map description
- Improved torpedo movement
- Improved overkill bullet handling
- Added Strategic Missile Submarine (T3)
- Added Naval Transports (T1 and T2)
- Added Torpedo Launcher (T1)
- Added assist for attacking buildings
- Added complete map vision for defeated players
- Added a new camera system
- Added two hints
- Added the ability to disable mobile shields
- Added thematic music for peace / war
- Constructing T4 units can no longer be cancelled
- Changed the ACU and Support Commander attacks
- Increased the Heavy Air Transport (T3) HP
- Increased the Point Defense (T1) HP
- Increased the Torpedo Bomber (T2) range
- Increased gravity
- Reduced damage for units in an attacked transport
- Reduced Omni Sensor Array (T3) range
- Fixed some shield damage bugs
- Fixed some bullet move bugs
- Fixed another torpedo target restriction bug
- Fixed an air crash bug
- Fixed a transport slow bug

Version 8:
- Removed the transport slot in a Heavy Gunship (T3)
- Increased the Heavy Air Transport (T3) HP
- Fixed a bug in the torpedo targeting restrictions
- Fixed the Radar (T1)
- Improved Team Placements
- The Phantom now receives twice the normal income
- Changed the hotkey for Assist
- Increased all cooldowns and damage values to reduce lagg
- Added a Team Defense mode

Version 7:
- Improved some attacks
- Improved Collision Shapes
- Improved Shadows
- Improved Strategic Missile Defense
- Improved the CZAR model
- Improved the target restrictions for torpedoes
- Added salvos of projectiles for some units
- Added a Standard Class
- Added mana costs for some attacks
- Added Tactical Missile Defenses
- Added Anti-Torpedoes
- Added Mobile Missile Platform (T3)
- Added Heavy Air Transport (T3)
- Added Heavy Gunship (T3)
- Added Shield Boat (T3)
- Added Torpedo Boat (T2)
- Added Strategic Missile Submarine (T3)
- Added a mode to start with a Paragon (T4)
- Added the engine version to the map name
- Added adjecency bonuses
- Added veterancy
- Reduced the Support Commander's (T4) death nuke
- Only Light Assault Bots (T1) can fire from transporters
- Transported units now fire automatically
- When a transporter dies, transported units are no longer slowed
- Fatboy now regenerates its shield
- Amphibous Tanks (T2) now cannot be targeted by torpedoes
- Changed the unit names to fit original names
- Some units can shoot their primary weapon while moving

Version 6:
- Improved the AI
- Improved the shield effect
- Improved some effects
- Improved Anti-Air of Strategic Bomber (T3)
- Improved Anti-Air of Battleship (T3)
- Increased the fly height of air units
- Reduced Bomber (T1) damage by 50%
- Added CZAR (T4)
- Added Fatboy (T4)
- Added a missile attack to the Air Superiority Fighter (T3)
- Added Fighter / Bomber (T2)
- Added a transport slot to the Gunship (T2)
- Added unit formation ranks
- Weapons do not have an attack field of 360° any longer
- Transported Bots can now fire out of transporters
- Transported units take 25% of the transporter's damage
- Fixed the unit portraits
- Fixed the kill counter
- Fixed some unit colors

Version 5:
- Added a prebuilt units mode
- Added a phantom mode
- Added a victory message
- Added the gatling bot
- Added the mass and energy storage
- Added a weak AI
- Esc changes the camera for dead players
- Reduced standard camera distance
- Fixed a repair bug
- Fixed some text bugs

Version 4:
- Esc no longer changes the camera distance
- Esc aborts unit production even without ressource supply
- Engine allows deep water
- Low-range units now move to enemies to attack them
- Changed AOE to exact Supreme Commander values
- Reduced Radar ranges by 12%
- Shield Generators can be deactivated to save energy
- Shield Generators have a constant use of energy
- Shield Generators have an increased regeneration
- Shield Generators cannot regenerate while attacked
- Shield Generators need a minum mana amount to reactivate
- Mobile Shield Generators have higher ranges (30%)
- Added Experimental Generator
- Added Experimental Artillery
- Added a Nuke Warning
- Added Overcharge ability for the Commander
- Added an ability to the Commander to change the camera
- Added an ability to the Commander display unit ranges
- Added Firing Randomness while moving
- Added a hint to supcom.btanks.net
- Added a help system
- Added timestamps to some messages
- Improved the Strategic Missile Defense
- Improved the flying arc of projectiles
- Improved performance
- Improved special effects
- Improved most of the terrains
- Fixed tree destruction for all types of trees
- Fixed a hotkey bug (Take Over)
- Fixed the little height difference for projectiles near the shore
- Fixed a damage bug for units with a high vertical collision offset
- Fixed some other bugs

Version 3:
- Rescaled Ranges (15% reduction)
- Added acceleration for units
- Fixed a torpedo bug
- Rebalanced Aiming
- Improved Tooltips
- Fixed some text bugs
- Reduced the damage dealt by bombers by 75%

Version 2:
- Nuclear Explosion damage spreads over time
- Mass Fabricators are rebalanced: Costs and income are now an average of Supreme Commander and Forged Alliance

Version 1:
- Initial Release
- Includes lots of supreme commander features like the ressource and projectile systems, 3 tech levels and experimental units.