Yes, Sergeant Major is still a rank in the Army. It is the highest enlisted rank in the U.S. Army and is typically held by senior non-commissioned officers who have extensive experience and leadership skills.
Edgar Allan Poe held the rank of Sergeant Major in the Army.
There is no such rank as Medic Sergeant Major of the Army. There is a Sergeant Major of the Army and regardless of his specialty, it is just SMA.
No, there is no rank of "Major Sergeant" in the Army Rangers. The ranks in the U.S. Army Rangers follow the same structure as the rest of the Army, including ranks such as Private, Sergeant, Lieutenant, Captain, and Colonel.
Sergeant Major of the Army is the highest rank NCO.
Command Sergeant Major is the highest enlisted rank in the US Army
Sergeant Major of the Army
There is a Command Sergeant Major rank in the US Army and US Marine Corps. There is no "Command Sergeant Major Leader" rank, however.
It's a rank - Command Sergeant Major
Anyone in the US Army can lose their rank - in the late 1990s, the Sergeant Major of the Army was demoted. It's not as easy for an SFC to lose their rank as, say, a Specialist or Sergeant, but it can happen.
FORSCOM does not have it's own Sergeant Major of the Army - there is only one SMA in the entire Army. The Command Sergeant Major of FORSCOM holds the rank of Command Sergeant Major, and this post is currently filled by CSM Ronald T. Riling. The current Sergeant Major of the Army is SMA Kenneth O. Preston.
Technically, all officers are of a higher rank than any sergeant. Sergeant Major however, is a very high enlisted rank. A sergeant major will usually only take commands from a Lieutenant Colonel or higher.
Which Navy did you have in mind? There is no such rank in the US Navy. Command Sergeant Major is a high enlisted rank in the US Army, and denotes the senior NCO of whatever unit or element they hold the position in (it can be anywhere from Battalion to Army level).