What they would be good as was escort cruisers for the troop convoys that would be needed to take the army all through South East Asia and beyond.
Below: Ning Hai as built 1932.
Ping Hai as last seen in Chinese colours before being sunk by the Japanese and then raised, and repurposed as one of the Ioshima Class.
Having the original building plans available made it easy for the Japanese to plan what they wanted to do with the two ships. Like all Japanese ships built during the mid-1930's, the ships had stability problems. The need was to alleviate these problems and make the ships useful additions to the fleet.
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Fitted with bulges to give better stability. The Japanese Navy accepted the loss of 2 knots to fit the bulges and in turn fit a very useful heavy AA armament that would make their role as escorts much easier. One twin 5" dual purpose turret on the bow, then twin open backed mountings (much lighter than the turret) in the other three positions. 25mm light AA, and a pair of 21" torpedo tubes (not 24") rounded out a useful armament. The 25mm armament was added to with various amounts triple and single mountings.
Having the bulges did not improve their anti-torpedo protection, both ships succumbing to torpedo hits, one by submarine, the other by air launched torpedoes.
