Complex sentence: The Operational Training Unit (O.T.U.) was based at Ossington eight miles north-west of Newark and it was from bases like these, flying the Vickers Wellington, that all operational crew passed through on their way to squadron service.
Split into simpler sentences: The Operational Training Unit, home of the O.T.U. was based eight miles north-west of Newark. This was at Ossington, and it was bases like these, flying the Vickers Wellington, that all operational crew passed through on their way to squadron service.