In September 1914, Wade was commissioned as a captain in the Field Ambulance of the Scottish Horse Mounted Brigade. During initial training at Morpeth, he designed a mobile operating car, to "take the surgeon to the wounded". In 1915, his unit sailed to join the Gallipoli Campaign, and Wade operated using his mobile operating car at Suvla Bay. When Gallipoli was evacuated, Wade sailed with the Egyptian Expeditionary Force to Cairo. Here, he treated endemic infections such as malaria and schistosomiasis, to which the troops of the force were vulnerable. Wade took 400 photographs of the Mediterranean and Palestinian campaigns. He wrote a moving tribute, "The Flowers of the Forest," to the 58 Edinburgh students and doctors who enlisted with him in 1914.