The 7th Mordion regiment join Lady Augustus Stern by request of the High Lords as her personal company they bear her family colours as part of their standards and over the years remained loyal to only her and the Custodes she travels with. 

She is the reason they have the Rhinos, heavy guns, older sentinals and the jetbikes taken from her personal family armoury, she requested the superior fire of the ratlings as well as the techpriests and the small poenal battlion that travels with her.