Complex sentence: As work was drawing to a close in May 1943 the first squadrons started to arrive, the first being 342 (Lorraine) Squadron of the Free French Air Force within 2 Group from RAF West Raynham.
Split into simpler sentences: As work was drawing to a close in May 1943 the first squadrons started to arrive. The first was 342 (Lorraine) Squadron of the Free French Air Force within 2 Group from RAF West Raynham.