Complex sentence: The issue of the medium Vickers machine gun to Commando units set them apart from the rest of the British Army, where the Vickers Machine guns were more specifically used by specialist machine gun battalions in infantry divisions.
Split into simpler sentences: The issue of the medium Vickers machine gun to Commando units set them apart from the rest of the British Army. Where the Vickers Machine guns were concentrated in specialist machine gun battalions in infantry divisions.