I dug out my husband's WWII Navy separation paper. It is a 8x11 form with boxes and numbered typed answers filled in. The largest box in upper right hand corner has numbered answers 1,2,3,4 typed in. (are my notes)
xxx-xx-xx(1.Service number 7 digits) Name (2. Last, First, Middle) Rate (3. At time of separation ie Seaman, First Class USNR) Permanent mailing address (4. Home/mail address afterdischarge or could be address before enlistment)
then box 5. Place of separation, box 6. Type of discharge box 7. Address from which employment will be sought boxes 8,9,10, 11 (vitals ie race, sex, marital etc). Box 12 place of birth Now box 21 is a listing of all ratings held (from enlistment to separation) Box 23 is name of Navy Schools attended. Box 24 lists all service vessels and stations served.
So the answer to you original question should be typed in Box 24. If you are seeing just the "7th Fleet, Com Ser Navy 3205" then that was his duty "station". He did not serve on a ship or at least be officially assigned duty on any Navy "Vessel".
I also have a memory that "Com Ser" is short for Company Service, or Commissary Service, since my dad was in the Navy Supply Corp, but pretty sure it is used for land based duty stations. My dad was a "lifer" and had more land based duty stations than vessel ones.
I will look thru the Navy muster rolls again but the numbers you gave are not 7 digit or spaced right. The 313412 is close but has a number missing and should be typed as 313-41-2? .