One piece was that the troops protecting the coast "east of Olympus" were supposed to withdraw during the night of 18 to 19 April. The 1st Armoured Brigade was going to "cover the final withdrawal across Thessaly".
The New Zealand Division would get to use the coast road. They would travel from Volos to Lamia.
The 6th Australian Division and the 1st Armoured Brigade would take the main road via Pharsala.
The plan was for marching soldiers to be carried on "motor transport".
The planners in Athens were moving ahead quite quickly. As early as 13 April, they had told Admiral Cunningham that "the evacuation of Greece was imminent".
The next day, General Wavell's staff had made a plan for "embarking the entire British force".
One factor affecting the withdrawal was that the Germans had now control of the air "in the forward areas". On the 15th, the Germans staged an air raid that destroyed ten Blenheim bombers on the ground. This had happened in the Larisa area.
The Germans also bombed Blamey's headquarters. The aircraft had been moved after the attack so that they were no longer available to provide support to the ground forces. This is based on the account in "Greece, Crete, and Syria" by Gavin Long.