The evacuation from Crete started on the night of 28 and 29 May 1941. The navy was expected to rescue the 20,000 soldiers on Crete, 4,000 from Heraklion and 16,000 from the beach at Sphakia. In fact, the situation was so dire and communications were lost that some were never informed. Colonel Campbell and his men at Retimo surrendered on 30 May, after they were running out of ammunition and food.
On the first night, Captain Arliss, with four destroyers, took 700 men from Sphakia and carried them back to Alexandria. At Heraklion, three cruisers and six destroyers were under attack. The destroyer Imperial took a near miss and the cruiser Ajax was damaged enough to have to withdraw. Still, by 3am, the ships had evacuated 4,000 men and were headed for Alexanderia. The Imperial's steering gear failed and she was sunk. That delayed the withdrawal, and they were caught in daylight. In the attacks, about 800 of the soldiers evacuated were killed.
This is based on the account in Vol.II of the Official History.