World War I U-boats with snorkels

What changes if German submarines possess snorkels during World War I?

Allied aircraft become less effective because U-boats can recharge while submerged, forcing earlier development of ASDIC or allowing the submarine campaign to gain much more leverage.

A snorkel reduces the need to expose a submarine on the surface, where aircraft and lookouts can find it. Without mature sonar, the Allies would have to accelerate underwater detection while facing a harder convoy-defence problem.