While the details of the ship 's fire @-@ control instruments are not fully available , it is known that the ships were fitted with a fire @-@ control director after completion . No computer was fitted at that time and data from the rangefinders had to be processed manually . Turrets 2 , 3 , and 5 were built with imported 6 @-@ metre ( 19 ft 8 in ) Bausch & Lomb rangefinders . These were felt to be inferior to the British Barr & Stroud instruments used on other ships and were removed in 1920 . They were replaced by either the British rangefinders or domestically built instruments of 6 or 8 metres ( 19 ft 8 in or 26 ft 3 in ) length . In the late 1920s the fire @-@ control systems were upgraded and additional platforms were added to the foremast to accommodate them . A pair of directors for the 12 @.@ 7 cm AA guns were added , one on each side of the forward superstructure , in the early 1930s . The fire @-@ control systems were again upgraded in the mid @-@ 1930s and directors were added for the 25 mm AA guns . Both ships had 10 @-@ metre ( 32 ft 10 in ) rangefinders installed at the top of the pagoda mast at that time . Type 21 air @-@ search radars were installed aboard the sisters in mid @-@ 1942 .