Early in the war before radar they ran submerge in daylight hours and ahead slow cause the periscope could leave quite a trail at standard speed and aircraft could still spot the trail from a mile or more.
At Dusk they would surface again.
Once SJ radar was available they would stay up all day because at seven miles it gave enough time to safely get under.
Japan ha no radar equipped fighters so fining you at night was damn near impossible and almost never happened. Edit your air file accordingly
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