At the outbreak of the Civil War in 1936 Tella, a Major, commanded a column of General Juan Yagüe's Army of Africa in its drive north from Seville. His outstanding success was the Battle of Mérida, on 11 August, in which his defence of the city enabled the bulk of Yagüe's army to move against Badajoz without being outflanked. He then took part in the Siege of Madrid.