Major Yamada returned to the base.
He was promoted to major in the army.
海軍の少佐が艦橋に立っていた。
The navy lieutenant commander stood on the bridge.
彼は三年で少佐に昇進した。
He was promoted to major in three years.
大尉 is the rank one level below 少佐 (captain/lieutenant vs. major), so learners often misorder these two in the rank hierarchy.
大佐 (colonel) is two ranks above 少佐 (major), and the identical 佐 suffix in both words causes confusion about which is higher.
From 少 (shō, 'lesser') + 佐 (sa, 'assistant'), a Sino-Japanese compound used in modern military rank terminology.