Comments by "Sar Jim" (@sarjim4381) on "Shōkaku and Cavalla, a Confrontation of the WWII Pacific Theater" video.

The Cavalla was one of the first WWII submarines to have a periscope mounted version of the SJ radar. This allowed Cavalla to only have the periscope above the sea surface about 20 seconds before finding an accurate fix on the Shokaku. It was able to enter the fix data in the TDC and have a more accurate fire control solution that in earlier subs. Because the position of the Shokaku was so accurately fixed by radar before the torpedoes were fired, Captain Kossler was able to use the radar again when he searched for the Shokaku. When the ship was nowhere to be seen in any of the predicted ranges from the radar, he could be fairly confident the carrier had actually sunk. It was the first time in the war that a submarine wasn't solely dependent on visual ranging through the periscope to find and sink a ship. Later improvements allowed the radar to work as far as 3 meters below the surface so there was no need to have the periscope break the surface and leave a distinctive "feather" behind.
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@phil4826 Yes, it was even more amazing in 1945. It obviously didn't have anywhere near the range compared to being six feet above water but, by manually focusing the SJ radar screen and increasing the output power, it could search about 15 degrees for about two miles at six feet below the surface. Once a target had been spotted with the periscope radar, the separate SJ was able to track it as long as the target was within that two mile range. Obviously a pretty handy thing compared to having to constantly raising the periscope and expose your position. Since the SJ was centimetric radar, the frequency was far above any kind of detector the Japanese had until about a month before the end of the war. Because of that, our subs had no fear of being detected by the radar emissions. The Japanese had the technical ability to develop more advanced radar and sonar. The constant infighting with the army over who would develop what kind of technology plus the IJNs seeming inability to understand why such technology was necessary doomed the Japanese fleet. [Edited for my usual typos and grammatical errors]
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