Lesson 05 of 16 Phase 1: The military system
Military Units Explained: Sizes, Commanders, and Where the Legal Offices Sit
In this lesson: 3 sections
Army units nest from a squad of about nine soldiers up through platoon, company, battalion, brigade, division, and corps, and each level has a commander whose rank rises with it. For a legal matter, three levels matter most: the company or battalion where things start, the brigade or installation that can convene a special court-martial, and the separate brigade, division, or higher command that holds general court-martial authority.
Sources checked: September 26, 2026
Army units by size
The figures below are typical ranges, not fixed sizes. Unit strength varies with the type of unit and what is attached to it.
| Unit | Typical size | Usually commanded or led by |
|---|---|---|
| Fire team | 4 soldiers | Sergeant or corporal |
| Squad | About 9 soldiers | Staff sergeant or sergeant |
| Platoon | About 42 soldiers | Lieutenant, with a platoon sergeant |
| Company (battery, troop) | 62 to 190 soldiers | Captain, with a first sergeant |
| Battalion (squadron) | 300 to 1,000 soldiers | Lieutenant colonel |
| Brigade | 3,000 to 5,000 soldiers | Colonel or brigadier general |
| Division | 17,000 to 21,000 soldiers, more with attachments | Major general |
| Corps | 20,000 to 45,000 soldiers | Lieutenant general |
| Field army | Varies | General or lieutenant general |
Source for the table: <a href="https://en.wikipedia.org/wiki/StructureoftheUnitedStatesArmy”>Wikipedia, Structure of the United States Army. An older description from the Council on Foreign Relations gives companies of “130 to 150 soldiers” and brigades of “3,000 to 5,000 troops, generally three-plus battalions, led by a colonel” (CFR, 2006); the difference in company size is a reminder that these are approximations.
The Marine Corps uses the same ladder of names at the lower levels. The Air Force organizes by squadron, group, and wing, and the Navy by ship, squadron, and fleet; federal law uses those names when it assigns court-martial authority (10 U.S.C. 823).
Where legal authority sits in the ladder
The levels that matter for a legal matter are the company or battalion, where nonjudicial punishment starts; the brigade, regiment, installation, or wing, which can convene a special court-martial; and the division, corps, separate brigade, or fleet, which can convene a general court-martial (10 U.S.C. 815, 10 U.S.C. 823, 10 U.S.C. 822). For covered offenses committed on or after December 28, 2023, the decision whether to refer the case to trial belongs to special trial counsel rather than to any level of this ladder (10 U.S.C. 824a). Who holds each authority, including special trial counsel, and why decisions move up the ladder, is covered in how military organizations work.
Where the legal offices are
Several legal offices serve an installation, and they are not in the same chain:
- The staff judge advocate’s office serves the commander. Army doctrine makes the “staff judge advocate (SJA)” part of “the commander’s personal staff” (FM 6-0, Appendix C), and Fort Riley’s office describes its mission as providing commanders “timely, accurate, principled legal advice” (Fort Riley OSJA). At a court-martial, “Trial counsel shall prosecute cases on behalf of the United States” (RCM 502).
- Special trial counsel prosecute covered offenses, the most serious crimes, and “are independent of the military chains of command of the victim and the accused” (U.S. Army OSTC).
- Legal assistance can sit inside that office. At Fort Bragg, for example, the Legal Assistance Office sits within the XVIII Airborne Corps Office of the Staff Judge Advocate (Fort Bragg).
- Defense counsel have their own organization. In the Army, “Under the Chief of TDS, there are eight Regional Defense Counsel (RDC) responsible for overseeing defense services within a geographic region,” each overseeing field offices, and installation commanders provide support to defense counsel “regardless of the lack of a command relationship” (<a href="https://en.wikipedia.org/wiki/UnitedStatesArmyTrialDefenseService”>Wikipedia, U.S. Army Trial Defense Service). The Marine Corps and Air Force defense offices describe the same separation from local command.
Which office to call for which problem is sorted out in the problem-to-office table.
To find the right door on an installation, identify the unit and its level first, then ask for the office by name: defense counsel, legal assistance, or the staff judge advocate. If you are a civilian visiting, getting through the gate as a visitor comes first. This page describes the general Army structure; a specific unit’s organization may differ.