Which of the following ranks is classified as a non-commissioned officer at E-5?

The rank classified as a non-commissioned officer at E-5 is the Staff Sergeant. This rank holds significant responsibilities in the Army, including leadership, mentoring, and the supervision of soldiers. As an E-5, a Staff Sergeant is expected to lead a team and play a vital role in the operational readiness and effectiveness of their unit.

While the other ranks mentioned also carry non-commissioned officer status, they are not classified at the E-5 level. Corporals, while also non-commissioned officers, are considered E-4. Sergeants are E-5 but since the question is asking for the rank specifically designated as E-5, it doesn't fit here. Master Sergeants, on the other hand, are at the E-8 level and have even more experience and responsibility. This makes the Staff Sergeant rank the correct choice when identifying the non-commissioned officer at E-5.