The sail-less sub is not going to happen until somebody figures out a way to get sensors and other necessary devices into the hull.
Along with providing streamlining and protection for sensor, antenna, snorkel, and other masts, the sail also provides a margin of safety and stealth when coming to periscope depth for any reason. Imaging having no sail, and then coming to PD in rough seas to copy the submarine broadcast. You'd have to come so shallow that the rough seas would toss you around enough to broach the surface - then your whole topside is exposed. Bye-bye stealth!
Even with the current moderately-sized sail, subs broach in rough seas, but mostly it's just the sail (a much smaller visual/sensor target than the whole sub!) that breaks the surface. It happens. The better the driving team, the less it will happen, but it's going to happen anyway.
The reasons for reducing or eliminating the sail were reduction of drag, and reducing the possibility of the sail acting as a big giant stern plane (control surface) at high speeds. However, the other reasons mentioned above trumped these, and small(relatively speaking) sails were retained. You should see the difference in size between the Permit-and-later-class sails, and the Skipjack and earlier SSN sails.
I can hear it now: "Why not put the sensors in a UUV or pod on a tow-cable that you let float to the surface?" For one thing, a cable can break or be fouled, rendering the UUV/Pod useless. For another, a UUV/Pod will be less stable at PD or the surface than the sub itself, more at the mercy of rough seas than the larger platform. Additionally, the UUV/pod still doesn't answer the question of what to do about the snorkel mast, which is one of the most important pieces of emergency equipment on the sub. It serves to ventilate in case of fire or toxic gas, and also provides air to the emergency diesel engine.
TG
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