The army depended on the navy for being able to evacuate Greece in later April 1941. The RAF was pursuing an independent plan, as the situation went into collapse. As long as they could use airfields near Athens, they flew out the pilots and technicians. When the Blenheims were moved to Crete, they took as many as they could. Others were flown out by No.216 and 267 squadrons flying Bombays and Lockheed Lodestars. Flying boats, probably Sunderlands, were also used. The Wellingtons had already been withdrawn, s they were too vulnerable on the ground. Remaining RAF personnel would leave with the army.
The army plan was to move at night, as the Germans were not operating at night, to the relief of the British. Troops would move into position during the dark, and hide. Towards night, they would destroy equipment that they planned to abandon, and then move to the beach. Admiral Pridham-Whipple's force included the amphibious transports Gelnearn and Glengyle, which were equipped with landing craft. There were also 19 troopships and four "A-lighters". The A-lighter was an early LCT.
The ANZAC corps had been in a defensive position at Thermopylae since 19 April.
As the situation progressively got worse, partly due to the collapse of the Greek army, German air dominance became increasingly a factor. Not only did it complicate the withdrawal, but over the next month wrote off many of the Royal Navy's assets in the Eastern Mediterranean.
This is from Vol.II of the official history.