Complex sentence: They were primarily a repair and overhaul shop, but also a construction shop for other companies' designs, notably the Supermarine Seafire the company also undertook contract work for the Air Ministry, Lord Rootes, Shorts and Armstrong Siddeley worth £1.5 million.
Split into simpler sentences: They were primarily a repair and overhaul shop, but also a construction shop for other companies' designs, notably the Supermarine Seafire. The company also undertook contract work for the Air Ministry, Lord Rootes, Shorts and Armstrong Siddeley worth £1.5 million.