Amaya wrote:After the Heresy no commander is allowed to have command of both Imperial Navy Fleets and Imperial Guard Regiments in order to prevent wide spread future rebellions. In addition, Imperial warships have their own on board security forces known as Naval Armsman.
This. The change happened because, commanders with both a ground force and a ship/fleet would conquer a world for their own after
HH, and the High Lords of Terra (or was it Guilliman) separated the two so that no general haves that kind of power to abuse. In the long term that led to quite the rivalry between the
IG and IN and conflicts between troopers from both sides are common when transporting
IG units (normally small things such as bar fights). However they are easily contained and judged by a member of the commissariat who haves the most say in the matter despite the ship captain being in charge of the ship and all hands on it while in space and having the ability to outweigh an order/s from the Lord general/General in command of the
IG regiment/s.