Master of the Forge
The Master of the Forge has the same intermediate statline as the Chaplain and Librarian, though he swaps a point of WS for a point of BS. He also comes with artificer armor and a servo-harness. He’s not much of a combat character, but he can be our shootiest HQ choice because he can take a conversion beamer. Because this is a heavy weapon that is heavily reliant on range to be dangerous, it’s best to pair a conversion beamer with a bike so that you can get to the best firing positions.
The Master of the Forge has Blessings of the Omnissiah, allowing him to repair your vehicles, and Bolster Defenses, allowing him to increase the cover saves offered by terrain in your deployment zone. The main reason that you will take a Master of the Forge is Lord of the Armory, which allows him to take any type of Dreadnought as a Heavy Support choice as well as an Elite choice. If you want a Dreadnought heavy army, the Master of the Forge allows it. This is particularly devastating if you take a drop pod army, as six drop podding Dreadnoughts are incredibly hard for many armies to deal with, especially since many armies don’t bring much anti-armor firepower.
The Master of the Forge obviously pairs well with Iron Hands Chapter Tactics as it gives him a bonus to his Blessings of the Omnissiah rolls. In addition, it will grant It Will Not Die to the many Dreadnoughts that will probably be included in his list.
The Techmarine is a standard Marine version of the Master of the Forge, with a Tactical Marine’s statline along with artificer armor and a servo-arm. He comes with the same Blessings of the Omnissiah and Bolster Defenses rules. You can take one Techmarine for each HQ choice you take in your army, and he doesn’t take up an FOC slot. He can upgrade his servo-arm to a servo-harness as well as take a squad of Servitors armed with servo-arms. These help him with his repair rolls, or they can take heavy weapons to act as fire support.
The Techmarine doesn’t have a great niche in the current codex. He’s best used with a squad of Servitors with servo-arms to repair important vehicles. The Servitors aren’t a very efficient firepower unit, so you’ll usually be better off spending your points on Devastators or tanks. Finally, he does allow you to take a 2+ save character without taking up an FOC slot, which can be useful for tanking wounds. In particular, you can add another 2+ save to a bike mounted Command Squad and not care much if he dies. He can also provide add some extra firepower to a drop pod squad while protecting them from damage with his artificer armor.
Like the Master of the Forge, the Techmarine also benefits from Iron Hands Chapter Tactics.