On the Italian declaration of war on 10 June 1940, Dickinson had a force of two East African brigades of the King's African Rifles (KAR) organised as a Northern Brigade and a Southern Brigade comprising a reconnaissance regiment, a light artillery battery and the 22nd Mountain Battery Royal Indian Artillery (RIA). By March 1940, the KAR strength had reached 883 officers, 1,374 non-commissioned officers and 20,026 African other ranks. Wavell ordered Dickinson to defend Kenya and to pin down as many Italian troops as possible. Dickinson planned to defend Mombasa with the 1st East African Infantry Brigade and to deny a crossing of the Tana River and the fresh water at Wajir, with the 2nd East African Infantry Brigade.