Final answer:
Considering historical testimony, two or three ambulances per squad would be reasonable for an evacuation platoon, as this mirrors the responsibility shared by ambulance drivers in the historical context provided.
Step-by-step explanation:
The number of ambulances required per squad in an evacuation platoon can vary depending on several factors, including the size of the squad, the severity and number of injuries, and the efficiency and capacity of the ambulances available. From the historical context provided, it is known that Grace and the other drivers were each responsible for the maintenance of two or three ambulances. These ambulances were used in convoys to transport wounded soldiers from trains to general hospitals or to facilitate evacuations to hospital ships at Boulogne. Considering this, if the number of ambulances assigned to a squad is to maintain efficiency and ensure all wounded soldiers are transported in a timely manner, assigning two or three ambulances per squad seems reasonable, based on Grace's testimony.