Right. You see, it adds another facet depending on what you want to do.
If you are doing a literal translation from the spoken word into English, then "Mr. Lieutenant" is literal, and correct to what Minmay says.
But, if you are trying to interpolate what she says into English colloquialism, then you have to take into account that postfixes like, San, Sama, Chan, Kun etc. are basic parts of Japanese grammar that have been in place for centuries.
They are there to denote respect etc. towards the person you are speaking to. Does that mean that they are literally saying "Mr. Lieutenant" when saying Sho-i san?. No. It is engrained in the Japanese language to include those postfixes into greetings as a gesture of respect, but not really a literal translation, unless you do not know that person.
In normal civilian communications, I would more than likely refer to you as Mr. Hurin until you told me not to. But, were you a member of the military, I would definitely not call you Mr. Lieutenant, but merely, Lieutenant, or Lieutenant Hurin, as that is your rank and name.