He was promoted to colonel in the army.
In the navy, a captain often serves as the commanding officer of a ship.
He was promoted to colonel in his forties.
The rank of colonel is one level below general officer.
大佐 and 少佐 look similar in writing, but 大佐 outranks 少佐, which corresponds to major/lieutenant commander.
Standard kanji spelling for the rank of colonel or navy captain.
From Chinese-derived terms 大 (great) and 佐 (assistant, help), originally used in ancient Chinese official titles and later adopted for modern military ranks in Japan.