Field Grade officers are between the rank of O4 and O6; otherwise known as Majors, Lieutenant Colonels, and Colonels. In some occurrences, chief warrant officers 3 and 4 (CW3 & CW4) fulfill the position of field grade officers as well. Although the Army and Marines refer to this group by the name of field officers, the Navy and Coast Guard prefer to label this group as senior officers instead. While these two titles are similar, the term field officer is usually used to describe any officer who holds command of a theater on land. Meaning, they are in charge of units that are capable of operating independently. This is why Field officers are typically seen in charge of brigades, infantry battalions, artillery and/or cavalry batteries, etc.
