Techmarines often start as Marines with an aptitude for machinery; if they attract the notice of their Chapter leadership, they may be sent to Mars for a number of years to train with the tech-priests. After their training is complete, their armour is modified to fit their new servo-arms and backpack and is usually painted red to show allegiance to the Mechanicus - leaving only the pauldrons to display the Chapter colors and badge. This sets them apart from their battle-brothers and means they are not often completely trusted, though to technophilic Chapters like the Iron Hands it is a badge of honour.
When they return to their Chapter, Techmarines join their Chapter's Armoury and maintain the Chapter's vehicles and weapons. In some Chapters like the Salamanders all Marines know the basic maintenance procedures for their equipment, leaving the Techmarines free to work on more exotic weapons and war machines.
Among the Space Wolves, Techmarines are called Iron Priests, and will noticeably not paint their armour red, leaving it grey. The Iron Hands have two types of Techmarines. The first are Iron Fathers, who oversee the more "spiritual" aspect of the machine, like a Mechanicum version of Chaplains. The second rank is Ironwrought, who are full Techmarines.
A Techmarine's Power Armour is also modified to help work with his cybernetic enhancements and his armour's backpack is aupgraded with several robo-arms. His armour bears the rust-red colours of the Adeptus Mechanicus, but his Chapter badge is kept and displayed on one of the shoulder guards, so as not to piss off the armour's machine spirit, like the Death Watch. Techmarines are also able to wear full servo-harnesses. These are basically huge harnesses armed with robo-arms, plasma cutters, and flamers. Techmarines can also be accompanied by a retinue of Servitors; Gun Servitors, Combat Servitors, and Tech Servitors. Their usual weapon is a Power Axe with the Adeptus Mechanicus symbol on the head, as both a symbol of rank and as a weapon.
Warpsmiths are their evil counterparts among the Chaos Space Marines as well as Death Guard's variations, Biologus Putrifiers and Foul Blightspawns. Primaris Marines also get their own version of Techmarines.
According to Amberley Vail, in terms of personality, there is a strong tendency for them to be "somewhat eccentric at best" and as a result, chapters tolerate techmarines deviating from norms a bit. (Example of such deviance: Becoming friends with a human and eventually having sparing sessions with said human).
Dawn of War II
Relic Entertainment decided to use the the Techmarine in Dawn of War II as one of the three commanders for the Space Marines. The techmarine is the least aggressive of the marine commanders; he's built as a ranged unit (while the Force Commander and Apothecary are intended to lead assaults, he's expected to stand back and shoot things, and does inflict more damage shooting than they do), and focuses on improving ranged damage of friendly units, has abilities that support vehicles, and can bring emplacements that reinforce squads without needing to go back the base, along with bringing in sentry turrets. His style generally focuses on getting to a position and holding. He's trickier to use than the Force Commander and Apothecary, but his abilities can be quite deadly on certain maps, especially ones where he can place his turrets in strategically important locations that maximize what their firing arcs can hit while minimizing the directions the enemy can come at them.
|Forces of the Blood Angels|
|Command:|| Apothecary - Brother-Captain - Brother-Sergeant - Chaplain |
Chapter Master - Librarian - Sanguinary Priest - Techmarine
|Troops:|| Assault Squad - Devastator Squad - Sanguinary Guard - Scout Squad |
Tactical Squad - Terminator Squad - Veteran Squad
|Death Company:||Death Company - Death Company Chaplain - Death Company Terminator|
|Walkers:|| Contemptor-Furioso Dreadnought - Death Company Dreadnought |
Dreadnought - Furioso Dreadnought - Librarian Dreadnought
|Transports:||Drop Pod - Razorback - Rhino|
|Vehicles:|| Baal Predator - Land Raider (Land Raider Crusader - Land Raider Phobos |
Land Raider Redeemer - Land Raider Angel Infernus)
Predator Tank - Vindicator - Hunter - Stalker - Whirlwind
|Flyers:||Stormhawk - Stormraven - Stormtalon - Storm Eagle - Thunderhawk|
|Allies:||Space Marines - Primaris Marines|
|Forces of the Dark Angels|
|Command:|| Apothecary - Company Master - Interrogator-Chaplain |
Chaplain - Librarian - Techmarine - Deathwing Knight
Dark Angels Grand Master
|Troops:|| Assault Squad - Deathwing - Company Veterans |
Devastator Squad - Scout Squad - Tactical Squad
Ravenwing Black Knight - Watcher in the Dark
|Walkers:|| Dreadnought (Deathwing Dreadnought - Contemptor Dreadnought) |
Contemptor-Mortis Dreadnought - Mortis Dreadnought
|Transports:|| Land Raider (Land Raider Phobos - Land Raider Crusader |
Land Raider Redeemer - Land Raider Ares
Land Raider Solemnus Aggressor) - Rhino - Drop Pod
|Vehicles:|| Bike Squad - Razorback - Predator - Vindicator - Hunter |
Stalker - Whirlwind - Land Speeder Vengeance
|Flyers:|| Dark Talon - Nephilim Jetfighter - Stormraven - Storm Eagle |
|Allies:||Space Marines - Primaris Marines|
|Forces of the Grey Knights|
|Command:|| Brotherhood Champion - Grand Master - Librarian |
Techmarine - Chaplain - Apothecary
|Troops:|| Grey Knight Paladin - Interceptor Squad - Justicar |
Purgation Squad - Purifier - Strike Squad - Terminator Squad
|Walkers:||Dreadknight - Doomglaive Dreadnought - Venerable Dreadnought|
|Vehicles:|| Land Raider (Land Raider Crusader - Land Raider Vortimer) |
Rhino - Razorback
|Flyers:||Stormraven - Stormtalon - Stormhawk - Thunderhawk|
|Allies:||Inquisition - Sisters of Battle|