Complex sentence: Its performance in the 1948 war was however considered less than exemplary becuase the pre-independence Bureau was concerned with internal security matters, and was not set up for such its new remit.
Split into simpler sentences: Its performance in the 1948 war was however considered less than exemplary. This was due to the fact that the pre-independence Bureau was concerned with Internal Security matters, and was not set up for such its new remit.