So, I've been rewatching Star Trek:TNG, and Miles O'Brien is there occasionally. He's a Chief in TNG, and he's a Chief in DS9. Now, I was in the Navy, and I've always assumed that rankings in the Star Trek universe were based on the Navy. But I find it difficult to think that in the 14 years (7 for TNG and 7 for DS9) that Miles would never have been promoted. Is there any in universe reason given for this?
According to Memory Alpha, he actually WAS promoted:
Problematic Rank History
The character of Miles O'Brien, and the exact rank he held in Star Trek, has a history of its own spanning the length of the character's existence. In thirteen years of the character's appearances, only in the last four was his rank established to be presumably Senior Chief Petty Officer (although this term was never directly used onscreen). Through various other stages of the character's development, O'Brien was referred to as a Crewman, a Lieutenant, and various script notes indicated he was a "Warrant Officer."
This is based on 1994 "Shadowplay" episode where his title is stated to be "Senior chief specialist".
However, the whole story with his ranks seems to be one confusing ball of uncertainty, covered in detail in this Memory Alpha article. He had officer ranks shown or implied at some times (being called "Lieutenant", having officers reporting to him, wearing Lieutenant's pips; and holding Tactical Office position before Enterprise-D).