Complex sentence: On 1 June the RAF began to conserve its strength for the defence of Britain and a Minesweeper, a transport and three Destroyers were sunk and two destroyers were damaged in their absence.
Split into simpler sentences: On 1 June, the RAF reduced operations to conserve its strength for the defence of Britain. A Minesweeper, transport and three Destroyers were sunk and two destroyers damaged in their absence.