What’s the difference between SgtMaj & MGySgt? Why are there TWO E9 ranks in the Marine Corps? #SFMF

Why does the Marine Corps have two E-9 ranks? What is a Sergeant Major? What’s a MGySgt or Master Gunnery Sergeant? What’s the difference?

#urah #SemperFiMyFriends #marines #sgtmaj #mgunz #marinecorps #SFMF #ELI5USMC