Complex sentence: The only known submarines that used this arrangement was the Sjölejonet class boats where the guns also served as deck guns, being powerful enough to be used against smaller vessels, the AA guns were later removed as the subs were modified with streamlined conning towers.
Split into simpler sentences: The only known submarines that used this arrangement was the Sjölejonet class boats. The guns were later removed as the subs were modified with streamlined conning towers.