Complex sentence: By the time the unit was re-designated I. Gruppe, Schnellkampfgeschwader 210 in April 1941 the unit was based at Abbeville, undertaking missions against shipping and land-based targets.
Split into simpler sentences: By the time the unit was re-designated I. Gruppe, Schnellkampfgeschwader 210 in April 1941. Based at Abbeville, missions were against shipping and land-based targets.