Complex sentence: Halifax, between 1940 and 1945, was one of the busiest and most congested ports in the world and the Halifax Shipyard was already working at capacity handling repair work for Atlantic convoy ships damaged in transit.
Split into simpler sentences: Halifax, between 1940 and 1945, was one of the busiest and most congested ports in the world. Further, the shipyard was already working at capacity handling repair work for Atlantic convoy ships damaged in transit.