The Actual Number of Space Marines in a Chapter

[Beta galactosidase]

There are very different uses for tank crew, even in the same kind of tank, and that determines whether they are reserve company marines or not.  We have an old source and a modern one that support this from different perspectives. The old one is codex: ultramarines, and the modern one is chronus.  Codex: Ultramarines describes the two tactical reserves: "the Marines of the 6th and 7th Companies can also act as crews for large, independent formations of the various armoured vehicles deployed by the Chapter. Thus the Chapter is able to field entire companies of Land Raiders or Predator battle tanks, for example."  Chronus is a headquarters sergeant, and when large scale armored combat happens he can command up to 50 marines, i.e. 25 tanks, in battle.  Mass armored warfare is when reserve marines are used as crews, because it is an auxiliary function of space marines.

 

Reserve companies even when they are infantry are used as auxiliary functions.  When a battle company is assaulting an important target and enemy reinforcements are closing from the rear, it's the job of reserve tactical squads to hold them off, and reserve fast attack units to make a distracting raid on the enemy's flank, and of reserve tank crews to fight great big tank battles so that the battle company and veterans can hit the main goals of the battle.

 

Space marines are post-humans and everything has to be geared around delivering space marine infantry as effectively as possible.  A space marine tank company or naval squadron only so much better than a mortal human version.  While marine crews have superior training, experience, and technology, they are still a metal box with a gun, limited by their engines, and don't have the enormous advantage in speed and small effective unit sizes that marine infantry have over mortal troops.

 

Space marine tank crews usually have to be active infantry and from the same company that is using the vehicle. This is because usually, tanks are integrated down to the level of the demi-company in very tightly combined arms formations, not the mass deployments of armor described for Chronus and the reserves, which are exceptional circumstance, as supported by Chronus the Spear of Macragge being a somewhat irregular headquarters officer brought out for special occasions.  Instead, single predators are assigned in ones and twos along with only a few infantry squads. This is so they can be used to more effectively deliver the infantry.  In most uses in a marine chapter, a tank isn't even a separate cavalry asset at all, its an infantry weapon in the form of a tank.  When an infantry unit has a problem, they might not be able to solve it with a normal infantry lascannon, so they use a lascannon that can fire while moving 50kph and is immune to las rifles. Tank crew in that usage should come from the same company as the infantry because they are already integrated into the command structure, cult, and culture of that specific company and even demi-company.

[Captain Idaho]

3rd edition Codex Space Marines started the idea that vehicles were fully crewed.