(C1-thru-C4 correct?)
In the past, some of us have suggested using E4 or E5, the rank you would have should you exit without graduation. (and your monthly pay is less than an E-1)
BUT, Isn't there a Naval Academy tax drop off service there? I know West Point has (or had) one, and y'all are far to busy, and some of the questions about being in college (not really) are kind of subtle...the Drop-Off folks know the answers .. For instance, "Can your parents claim you as a dependent ?".... not in the 2nd-4th years you are there at the academy, and just rarely "sometimes" for the first year you are there.
What is the purpose of the question in the Personal Info interview wherein it asks about military paygrade, and why is it important for tax purposes? I ask because a midshipman at the US Merchant Marine Academy "shall be appointed by the Secretary of the Navy as a midshipman in the Navy Reserve (including the Merchant Marine Reserve, Navy Reserve)." See 46 USC Sec. 51311(b). Midshpman, however, are not cadets, warrant officers, or commissioned officers. TT, therefore, does not have a grade that is appropriate for cadets.
...the purpose of the Q about paygrade is that the various tax software versions are free for enlisted/ E-grades, but not free for warrant W- or officer O-grades. At one time it was only E5 and below.
In any case, unless you get a W-2 from the DOD for 2020, there would be no free tax software for you no matter how you indicate pay grade....if you do get one...I'm not sure what you do.....I'm not sure Merchant Marine qualifies...but this is a software provider software "discount" benefit for active duty military......not something the IRS uses..