I know it lasted for seven years. But no one -- not the guys writing the title for the show all the way up to the writers writing the episodes themselves ever referred to him as a Lieutenant Commander. It was always, always "Commander."
Mutarada:
Point well taken. However, it seems both costuming and title goofs are de riguer in Star Trek.
Take TOS. It's clearly established in later eps that Spock is a full commander, in dialogue and sleeve braid, but he is officially mentioned a number of times as lt. cmdr. in the first season despite having two full braids, denoting a full commander in the uniform of the time.
They also made this mistake with a character named Lt. Cmdr. Giotto, the security chief from
Devil in the Dark. He is definitely wearing full commander's braids, too. He should have worn the same braids Scotty and McCoy wore, a broken braid above an unbroken one.
The most famous being, of course, O'Brien from TNG then DSN. At first, he was an unnamed conn officer, then eventually became Transporter Chief O'Brien, but first he wore an ensign pip, then a full lieutenant's pips before getting a hollow pip that supposedly denoted a chief petty officer. In later seasons of DSN, they came up with a more stylized CPO pip for O'Brien that somewhat resembles a modern-day CPO's stripes.
And VOY was rife with them. As mentioned above, there was the mixup with Tuvok's pips and actual rank. First, he wore lt. cmdr.'s pips but was called lieutenant, then they fixed that, then finally promoted him to lt. cmdr.
And while it's true Chakotay was always referred to as just cmdr., his provisional rank pin does denote the rank of lt. cmdr. Perhaps that's the highest provisional rank a captain can give a non-member of Starfleet? Also, recall that Janeway's previous first officer was also a lt. cmdr, so perhaps the crew complement of
Voyager only warranted a lt. cmdr. as her first officer.
All this means that they messed up! Frankly, TNG and DSN, with the exception of O'Brien, were the only shows that were consistent with rank pins and titles, and maybe ENT, too.
Red Ranger