Good afternoon everyone Balloons should not be able to see submarines unless (1) the submarine attacks something within the balloon viewing range or (2) detected by flights of fighters on patrol over an ocean sector.
Historically the subs ran on the surface during the day and at night (balloons would have 0 visible range during night periods). When running on the day they did so while on the prowl looking for a target and when spotted would dive to attack. So if balloons can see subs all the time (which is woefully inaccurate for WW1 standards) then 50% of the game day all subs disappear from the screens unless they attack a target or if a patrolling fighter spots them.
The other 50% of the game day (daylight assuming good weather) they "could be spotted". Even if it is daytime, the WW1 submarine running on the surface in a standard sea state is really hard to spot. You have to be looking in the right spot for a period of time to be able to pick them up even at the horizon.
Recommend going back to the original rule to make it easier - subs are only spotted when they attack or when a fighter flight spots them while on patrol or flies over them.
Thank you for your time.