So here's some rank insignia I made for the armed forces of the Terran Union, the pan-Terran government (in theory, at least) in one of my science fiction projects. They are shoulder insignia; the bottom of each insignia should face forward, with the top facing backward. They would be rotated 90 degrees if displayed vertically.
All three services - the Terran Marines, Union Navy and Terran Spaceforce - use identical insignia.
The officer ranks of each service are:
Marines - Captain General, General, Lieutenant General, Major General, Brigadier, Colonel, Lieutenant Colonel, Major, Marine Lieutenant, Second Lieutenant, Junior Officer, Student Officer
Navy - Lord Admiral, Admiral, Vice Admiral, Rear Admiral, Commodore, Captain, Commander, Lieutenant Commander, Naval Lieutenant, Sublieutenant, Ensign, Officer Cadet
Spaceforce - Grand Marshal, Chief Marshal, Marshal, Vice Marshal, Junior Marshal, Flight Captain, Senior Leader, Leader, Flight Lieutenant, Flight Officer, Pilot, Officer Candidate
The enlisted ranks of each service are:
Marines - Sergeant Major, Master Sergeant, Color Sergeant, Sergeant, Corporal, Lance Corporal, Marine First Class, Marine, Recruit
Navy - Master Chief, Senior Chief, Chief, Petty Officer, Junior Petty Officer, Able Serviceman, Serviceman First Class, Serviceman, Listman
The Spaceforce has no enlisted personnel.
E1 - REC/LST has been intentionally left off, as E1s bear no insignia whatsoever.