Complex sentence: Bowyer Bell, in his history of the organisation, states that at the beginning of 1942 there were over 300 IRA volunteers in four companies constituting the Belfast unit, lead by the small group calling itself Northern Command.
Split into simpler sentences: Bowyer Bell, in his history of the IRA, states that at the beginning of 1942 there were over 300 IRA volunteers in four companies constituting the Belfast unit. These men were lead by the small group calling itself Northern Command.