Complex sentence: In modern military terms, an ordinary centurion was approximately equivalent to a Warrant Officer that had a junior officer's commission, whereas the most senior centurion was closer to the equivalent to the rank of a full Captain.
Split into simpler sentences: In modern military terms, an ordinary centurion was approximately equivalent to a Warrant Officer that had a junior officer's commission. Whereas the most senior centurion was closer to the equivalent to the rank of a full Captain.