Backstory
Navy Ranks:
Note - this generally refers to military ships. The NSS Cyberiad is a civilian station. The only ranking military personnel aboard as standard is the Captain.
Unlike the army/marines, Navy personnel aren't hired for their fighting prowess, but instead their technical knowledge and ability to operate a ship. The air force and navy are now merged, and a fleet of ships is easily enough to threaten most planets. While they may lack the ground forces for a full invasion, naval fleets have the high ground, and with a substantial nuclear or plasma arsenal can render cities into ash.
Admiral:
Is in charge of a fleet. Multiple ships and/or stations.
Currently the only established Admiral is Admiral Lem of Cyberiad Station's protective fleet.
Captain:
The master of a ship or station. They are the ranking officer aboard the station - unless orders come from Centcomm or an Admiral, their word is law. Assuming it is a legal order, that is.
Commander:
About the same as a Head of Staff, a Commander is given command over a department or group on a ship, such as the security team or engineering. Alternatively, may be in charge of a group of boats, such as a wing of fighters.
Lieutenant Commander:
Usually Appointed By a Commander to be a smaller part of staff, The Lt. Commander can fill many roles such as Combat Squads, or be a representative for NT. Usually a senior Lieutenant, who liaises with the commander on behalf of the other Lieutenants.
Lieutenant:
A commander of smaller groups, similar to the warden or QM. They have authority over a small area such as the brig or cargo.
Major-
Midshipman:
The standard rank. A single midshipman may be an engineer, or even a janitor. However, unlike a civilian crew they would be trained in the basics of combat and are subject to military law.
Army Ranks - DS, ERT etc.
The army consists of the fighting forces of NT - those who board and kill the xenos, revs, etc. Seperate from the ranks of the navy, they are often held in contempt by the Navy for being "dumb grunts". In return, they often think of the Navy as wusses who never involve their selves in a fight personally.
Captain:
Is in charge of a Company - usually about 250 people. Obviously they'll never be deployed with a full company on SS13 due to lack of space. While on board a naval vessel, a Captain is addressed as Commander.
Lieutenant:
The lowest officer rank. Is in charge of a Platoon - 50 or so people. 4 or 5 Sgts with squads under them.
Sgt:
Leader of a squad. Generally a Sgt will lead an ERT/DS team.
Corporal:
Minisquad leader. Aka Fireteam leader - in command of 4 or so Pvts and Specialists.
Specialist:
A private with a specialist function - eg, demolitions, medic.
Private:
The lowest rank, but still a soldier.