Are Submarines noticeable underwater

Answer 1

It depends on the water in the area of operation, but absolutely, especially from aircraft.

If close enough to a surface vessel and the water is clear enough, it can be seen as well, but not as easily.

Aircraft spotting of submarines underwater was a major concern for both Allied and Axis submarines during WWII, and the limited depth capability of those boats meant they were more susceptible to aerial attack even after they dove. T they're a lot harder to detect today (submarine sonar can pick up aircraft noise and thus either go deep or stay deep), though being detected in shallow water or clear ocean is still a very real threat. It's one reason that submarines have been painted black for decades - they're harder to spot.

Depending on the clarity of the water, submarines have been spotted from the air as deep as 400', but they're usually spotted at Periscope Depth, which is around 65' keel depth depending on the boat.

It's easier for aircraft to spot them in the clearer waters of the Pacific or the Caribbean rather than the Atlantic, but the operating depth of most boats is deeper than most aircraft can spot them anyway. You have to literally be over them and looking as well - again, black isn't easy to spot from the air against the darker background of deep ocean. Generally, the attempt is made by ASW aircraft to locate a boat by sonar (sonobuoys or dipping sonar from a helo), and then visual scanning is attempted. However, as an old submarine Sonarman, I can tell you that once an aircraft is picked up (a helo has to be low enough on the water to use dipping sonar that it can be heard, and sonobuoys make unmistakable splashes when they hit the water), a boat captain won't give an aircraft the opportunity to get a look.

As an example of the concern of being spotted from the air, during the Cold War when I was submariner, the onboard emergency buoy, which could be released in the event the boat sank in shallower water, was normally painted orange so it could be more easily spotted if released and on the surface (it had about 400' of cable). The buoy was painted black and welded to the deck if going on special ops in hostile waters so that it couldn't be spotted from the air.

All shiny metal surfaces are also painted black, so that sunlight can't reflect off of them and potentially alert an aircraft to a boat's presence.