Small comparison between Starfleet Ranks:
Next Generation era and modern Terran militaries,
by way of Babylon 5

Starfleet ranks in apparent order as shown in "The Next Generation",
showing position of Command (1) above Engineering (2) and Science (3),
from Captain to Crewman, not including Petty Officer:

Captain

Commander,1

Lt-Commander,1

Commander,2

Lieutenant,1

Lt-Commander,2

Commander,3

Lt. (junior grade),1

Lieutenant,2

Lt-Commander,3

Ensign,1

Lt. (junior grade),2

Ensign,2

Lieutenant,3

Lt. (junior grade),3

Ensign,3

Crewman (1+2)


However, the above ranks do not incorporate 'Petty Officer';
of which there are several grades in SF all or some of which
are apparently equivalent to the 'commissioned' ranks.

The above system is also slightly contradictory and adds
confusion between which ranks are commissioned and which
aren't as, for example,an Ensign must serve two years before
being promoted to Lieutenant, but must stay at junior grade
level for a further three years.

This is similar to the promotion structure in the
non-commissioned ranks of many Earth armies, with Starfleet
Lieutenant being roughly equivalent to a senior
Non-Commissioned or Warrant Officer.

Promotion in the Command and Medical Fields also requires further
training as well as promotion though merit. For example, Troi had
to pass a series of Officer training tests to be promoted to full
Commander.

All Ranks below, in order, in comparison with EFMC
ranks Babylon 5:


Firstly though, the use of non-commissioned ranks as an example
reflects the slightlyambiguous nature of non-command officers
and petty officers having some authority over junior officers
and so gives a better comparison between command officers and
junior officers.

It would seem that the 'yellow' ranks of Engineering and Security
plus the 'blue' rank of 'Commander' (i.e Med/Sci Commanders Crusher
and Troi) follow fairly closely the ranks used in the Security/Army
of EarthForce (which are loosely based on, and offer a good
comparison with, those of the existing present United States
Marine Corps) and can be incorporated into the
'Starfleet' command structure as follows:

Command (red)
1.Captain
2.Commander
5.Lieutenant-Commander
8.Lieutenant
11.Lieutenant (junior-grade)
14.Ensign

Engineering/Security and Medical
3.Commander=Colonel
4.Commander=Major
6.Lieutenant-Commander=Captain
9.Lieutenant=First Lieutenant
12.Lieutenant (junior-grade)=Second Lieutenant
15.Ensign=Command Sergeant-Major

It can be assumed that M/Sci ranks below Commander and above
Ensign are equivalent to the ranks of:
Senior, Master and Chief Petty Officer, giving:

1.Captain=Colonel

2.Commander=Major

3.Commander (2)=Captain

4.Commander (3)=First Lieutenant

5.Lieutenant-Commander (1)=Second Lieutenant

6.Lieutenant-Commander (2)=Senior Chief Warrant Officer

7.Senior Chief Petty Officer=Chief Warrant Officer

8.Lieutenant (1)=Warrant Officer (class 1)

9.Lieutenant (2)=Warrant Officer (class 2)

10.Master Chief Petty Officer=Command Sergeant-Major

11.Lieutenant (junior-grade)(1)=Sergeant-Major

12.Lieutenant (junior-grade) (2)=Master Sergeant

13.Chief Petty Officer=Gunnery Sergeant

14.Ensign (1)=Staff Sergeant

15.Ensign (2)=Sergeant

16.Ensign (3)=Corporal

17.Crewman=Private First Class

18.Crewman (2nd class)=Private

http://tgm.firstones.com/wiki/Earthforce_ranks