I'm pretty new to Warhammer 40k
, just started in 8th edition. I wanted to confirm some Astra Militarum regiment rules before I go out and start buying things.
If I run a spearhead detachment of Pask and all Cadian Leman Russ, I get the Cadian Regimental Doctrine: Born Soldiers for that detachment. If I run another Detachment of all Militarum Tempestus would I get the Storm trooper Regimental Doctrine for that detachment?
Correct. As long as the detachment is "pure" and meets the criteria for getting a doctrine, the detachment benefits regardless of what other detachments are doing.
You could take your Spearhead above and combine them with a Patrol of SPESS MAHRINES and the Spearhead will still get the doctrine.
Also welcome to the hobby!