Complex sentence: Only on 10 September did armoured cars of the 11th Hussars spot the Maletti Group advancing through the desert; a thick mist shielded the British and allowed them to observe the Italian concentration.
Split into simpler sentences: Only on 10 September did armoured cars of the 11th Hussars spot the Maletti Group advancing through the desert. A thick mist shielded the British and allowed them to observe the Italian concentration.