[CCIP]

Ah yeah, the underwater detection by planes can be an issue, although this is true only of mods which allow planes to detect you underwater (TMO, OM, not sure if RFB also does this). In default game, this does not happen. My tip: either go very deep, or keep your periscope+radar out while cruising underwater. Unless you have a way of detecting the planes above you, the TC will not go to 1x until you take damage. In TMO, I believe planes can see down to 60ft, although only from a limited range. In late-war Operation Monsoon play, this gets VERY tough as the planes have ways to hit you up to 100m depth (I presume a simulation of MAD gear and/or FIDO torpedoes). But you just deal with that I guess...