Complex sentence: Under the constant threat of Luftwaffe air strikes (which had sunk many Greek and British warships during the evacuation), the cruiser sailed to Souda Bay, Crete, then on to the UK naval station at Alexandria, arriving in Egypt on April 23rd.
Split into simpler sentences: Under the constant threat of Luftwaffe air strikes (which had sunk many Greek and British warships during the evacuation), the cruiser sailed to Souda Bay, Crete. Then on to the UK naval station at Alexandria, arriving in Egypt on April 23rd.