As a result of the threat from Italian forces in Italian East Africa, Platt's modest forces in Sudan were reinforced in late 1940 and early 1941, primarily by the arrival of the Indian 4th Infantry Division and the Indian 5th Infantry Division. In recognition of his larger corps-sized command he was promoted acting lieutenant general in January 1941. He commanded the forces invading Italian East Africa from Sudan during the East African Campaign. After re-taking the abandoned Kassala railway junction in Sudan on 18 January 1941, Platt advanced into Eritrea and captured Agordat on 28 January. He next faced strong Italian resistance at Keren. From 3 March to 1 April, Platt's leadership played a large part in the successful outcome of the Battle of Keren. The Eritrean capital, Asmara, was taken by the Indian 5th Infantry Division on 1 April while Keren was still being mopped up by the Indian 4th Infantry Division. After the battle of Keren, Platt lost the Indian 4th Infantry Division which returned to Egypt. On 8 April, the port city of Massawa surrendered. The forces still under Platt then marched on Amba Alagi.