the naval rank below captain is Commander
A Group Captain is an RAF rank, equivalent to a naval Captain and an army Colonel.
In the Army, the rank below Captain (O-3) is 1st Lieutenant (O-2). In the Navy, the rank below Captain (O-6) is a Commander (O-5).
1st Lieutenant (one silver bar)
There is no rank called "colonial." The rank "Colonel" is below General and above Lt. Colonel, Major, Captain, and so on.
Captain is 2 silver bars.
In the US and British armed forces, a Naval Commander is equivalent in rank to an Army Lt. Colonel and a Naval Captain is equivalent in rank to an Army Colonel. Please see the related links.
The next rank below that is Lieutenant Colonel. Below that is Major. Below that is Captain. Below that is First Lieutenant, and below that is Second Lieutenant. That's the Army, Marine Corps, and Air Force.
After the rank captain and captain grades 1, 2 and 3 is Major
"Lieutenant" is a rank in the military or police forces, typically below the rank of captain. It signifies a leadership position with responsibilities for a unit or group of personnel. "Lt captain" may refer to a combination of these two ranks, which may vary depending on the organization or country.
The rank "SN" signifies Seaman.
When you rank below that Captain, and you either pass them while outdoors, or while indoors and under arms.
Captain