What about sensors on floating platform connected by cable ? Some of such sensors are already researched .. like that floating up-looking fish-eye scope with computer corrected image. Radio wires and buoys are used even today. Sure .. snorkel is a
problem, but you don't need it that much.
Or something like UUVs equipped with cameras, RWR or Radar masts. Or even better, UAV (unmaned airborne vehicle) inside UUV, with both radar and cameras.
Or just long mast supported with wires .. like snorkel on german subs - folded backward on the hull (or inside hull cavity). With non-penetrating masts this is no problem.
I think the most important reason for sail is that there must be some place for watchmen in harbors. And sub-hull is not suited for that at all.
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