[Perused some older threads on this topic, had to bring it up again tho]
Just came across a major TF (running the 1.4 version of the latest TM for stock, plus a few other minor things) with 2 Hiryu class CVs in mid '43. (:hmm

I have a damaged boat with one rear torp, so I dared not mess with it. I kept track of numerous air patrols as the TF sailed past with my SD radar, but eventually they spotted me at periscope depth, so I went down to 160 (this in heavy seas), as per some older threads about TM. They spotted me again, so down I went to 250, where they spotted me and bombed me AGAIN! I finally risked going to 310, below the thermal layer, and prayed that my patchwork hull will hold together until nightfall.
Combined with the psychic all-seeing/hearing merchants who can spot your scope at 2000 yards on a moonless night in heavy seas, I might just go back to SH3. I'll try one more patrol with the new campaign layers mod, but this is downright silly; the British with all of their fancy technological doodads in the Atlantic would be envious of this kind of performance.