Complex sentence: The colonial army's heavy field artillery unit, the 301st FA Regiment which fought in Bataan, was equipped with GPFs and two 155mm howitzers--which were reportedly fitted with straight shields and wooden wheels.
Split into simpler sentences: The colonial army's heavy field artillery unit, the 301st FA Regiment which fought in Bataan, was equipped with two 155mm howitzers and GPFs. The howitzers were reportedly fitted with straight shields and wooden wheels.