Is it correct for a soldier to address an NCO as sir?

When addressing a superior officer (not a NCO), "sir" is used to replace the person's specific rank.

https://www.debretts.com/expertise/forms-of-address/professions/the-armed-forces/


In both the United States Military and British Armed Forces addressing an NCO as "Sir" is incorrect, and the almost universal response to such an address is "Don't call me sir, I work for a living".

In the Royal Canadian Mounted Police only commissioned officers are addressed as "sir", NCOs and constables are addressed by thier rank.

More follows:

https://en.wikipedia.org/wiki/Sir

In many militaries, Warrant Officers are classed as senior NCOs, and typically hold positions such as Sergeant Major.

They are addressed by lower ranks as "Sir" or "Ma'am"

Junior NCOs (Corporals, Sergeants and equivalent) are not addressed as sir.

https://en.wikipedia.org/wiki/Warrant_Officer