Re: officers are called 'sir'
There's also usage to consider. Mr and Mrs generally use the family name with the title. Used alone they sound oddly abrupt. Sir and Ma'am don't need a name with them when addressing someone.
We are quicksilver, a fleeting shadow, a distant sound... our home has no boundaries beyond which we cannot pass. We live in music, in a flash of color... we live on the wind and in the sparkle of a star! Endora, Bewitched