Complex sentence: The shortage of tanks in 1940, was reflected in the organisation of 31st Armoured, it would have one armoured and two motor brigades, which was changed at the end of 1940, to two armoured and one motor brigade.
Split into simpler sentences: The shortage of tanks in 1940 was reflected in the organisation of 31st Armoured Division, which first had one armoured and two motor brigades. At the end of 1940, this was changed to two armoured and one motor brigade.