Which of the following is NOT a rank in the Marine Corps?

The rank of Sergeant Major is indeed a valid and recognized rank in the Marine Corps, specifically referring to a senior non-commissioned officer rank that plays a crucial role in leadership and mentorship within the Marine Corps structure. This rank is responsible for overseeing the welfare and readiness of the junior enlisted Marines, ensuring that they meet the high standards expected in the Marine Corps.

Brigadier General, Captain, and Major are also valid ranks within the Marine Corps, representing different levels of command and leadership responsibilities. Brigadier General is a one-star general rank, Captain is an officer rank typically in charge of a company, and Major is a field-grade officer rank that serves as a key leader within battalions or similar units.

The correct answer identifies that each of the other ranks listed is indeed a part of the Marine Corps hierarchy, while conflating the specifics of Sergeant Major with its seniority level might cause a misunderstanding of what ranks are officially recognized. Hence, understanding the roles and hierarchy of Marine Corps ranks is essential for effective communication and operational success within the military structure.