Complex sentence: There were also anti-aircraft artillery (Marine Flak) batteries in Kristiansand, Bergen, Trondheim, Bogen, and Harstad; these were armed with 88-mm pieces.
Split into simpler sentences: There were also anti-aircraft artillery (Marine Flak) batteries in Kristiansand, Bergen, Trondheim, Bogen, and Harstad. These were armed with 88-mm pieces.