Complex sentence: Soon afterwards he was promoted to the rank of non-commissioned officer and in February 1818 he passed examinations to become a midshipman and was immediately assigned to the seconnd "Flotskiy Ekipazh" (Fleet Crew) of the Russian Imperial Navy Baltic Fleet.
Split into simpler sentences: Soon afterwards he was promoted to the rank of non-commissioned officer. In February 1818 he passed examinations to become a midshipman and was immediately assigned to the seconnd "Flotskiy Ekipazh" (Fleet Crew) of the Russian Imperial Navy Baltic Fleet.