Complex sentence: The British also had a battalion Matilda II infantry tanks that while slow, were also equipped with the 2-pounder; the armour of the Matildas could not be penetrated by Italian anti-tank guns or field guns.
Split into simpler sentences: The British also had a small number of Matilda II infantry tanks that while slow, were well armoured and also equipped with the 2-pounder. The armour of the Matilda tanks could not be penetrated by Italian anti-tank guns or field guns.