[neilbyrne]

I've been having the same problems detailed above with escorts zooming in from all quarters for no apparent reason. Two nights ago I encountered a very large convoy (6 columns of 5) east of Formosa. I made three attacks on these guys all using the same tactics just to make sure I wasn't being paranoid about uber capable escorts. In each case I would run around them on the surface. Get twelve or so miles ahead, go to radar depth and track them in until the closest escort was 8nm distant then go to PD and silent running. Oh yeah, this was all at night. The only strong escort was an OTORI, the rest were corvettes and trawlers. The OTORI was on the convoy's stbd wing so I stayed to their port. I had their speed from radar and I'd lay out a speed vs. bearing track on the main body so I would pick up any major course change and keep periscope obs. to a min. Layer depth was 230ft. None of these tactics, nor keeping the lead escort pointed made any difference. At about 4kyds fm the nearest escort, the closest three escorts would turn right at me. Happened every time. This is OCT '44.
So sonar detections are as hosed as periscopes. Here I’d like to go into sub detection by escorts with sonar. I have a lot of experience with this, and it is very difficult. It's why between us and the Brits, we built 1600+ destroyers/escort vessels in WWII. There is strength in numbers, because the individual capability just sucks. In 1970 ASW School, we were taught the capabilities of all the sonars then in the US surface fleet. There were still some WWII ships active, mostly old FLETCHERs and SUMNERs that hadn’t been through the FRAM (Fleet Rehabilitation and Modernization) refit that installed newer systems. As I recall, these old girls had the SQS-46V sonar. We did a day or two in the attack trainer using this system. In absolutely beautiful water, isothermal (no layer) to 400ft, it had a reliable detection range of 2000-2500yds. Now remember this was the best sonar we had toward the end of WWII. In worse water, it was less. And a good rule of thumb about subs below the layer is that range across the layer is no better than 33-25% of range above the layer so that an above layer range of 2kyds yields a below layer range of 650-500yds. The IJN had nothing better than this, and in my research in Morison’s 15 volumes History of USN Ops in WWII and Roscoe’s histories of US Sub & DD ops, I never found a sub detection at greater than 2,500 yds on active sonar. Most IJN detections were at 2,000 or less. On passive sonar, those sonars could detect thermal (steam/oxygen) powered torpedoes pretty well but close in to own ship; electrics not at all. The only condition when a sub on her battery would be at all vulnerable to passive detection was if she were cavitating her screws, normally at 7kts or more and only above 150ft depth, or at 15kts or more below 150 but above 300ft. Deeper than 300ft, water pressure keeps the cavitation bubbles from forming. And even those detections were a long way from a sure thing.
Max sonar speed for WWII escort ships was 10-12 knots and it was not graceful degradation above that. From 10-12, count on losing half your range, go faster and you were deaf as a post in both active and passive.
The idea that the IJN could passively detect a non-cavitating sub on her battery is fantasy. The USN did not field a surface sonar with a really decent passive capablilty until the SQQ-23 (PAIR) IN 1969. PAIR had two completely rubber sonar domes, much more acoustically transparent than the conventional steel and enormously improved signal processing and displays. The PAIR test ship was USS BROWNSON (DD-868) in which I was CIC and then ASW officer. We took PAIR thru OPEVAL, the tests required to determine acceptance for service use. The sub we tested against was USS JALLAO (SS-368) a BALAO GUPPY. We did months of test runs together. JALLAO would open range on us with all her top hamper, periscopes, radar, comm antennae way out of the water so we could track her out to ~30kyds on radar. Sonar was kept in the dark as to her position. Then she would turn toward us and energize an acoustic augmenter to sound like a Soviet nuke boat. CIC would pass word to sonar the run had commenced and they'd try to detect. PAIR passed OPEVAL based on the results, but the reason I went into all this detail is that on the conclusion of the run, JALLAO would secure the augmenter and she'd be GONE off our sonar displays. I mean we wouldn't even have to wait for her to tell us she'd secured; we knew immediately.
So there we were in 1970 with a state of the art sonar, rubber domes, cabinets full of jacked up signal processors, JALLAO shuts down the augmenter and we can't detect her just on her battery. Plus detecting her on battery wasn't even part of the PAIR spec because everybody knew it couldn't be done. Even today, conventional subs on battery are the hardest passive ASW target there is. The idea the IJN could passively detect twenty-five years earlier is fanciful.
So where are these 4kyd detections coming from? In reality they can't be active or passive sonar or periscope detections at night; so what are they?

My mods:
Generic Mod Enabler - v2.6.0.157
1_TriggerMaru_Overhaul_2-5
1_TMO_25_small_patch
RSRDC_TMO_V502
RSRDC_V5xx_Patch1
Convoy Routes TMO+RSRD
1.5_Optical Targeting Correction 031312 for RSRDCv502
1.5_OTC for 16 to 9 Aspect Ratio RSRDCv502
Improved Stock Environment_v3_TMO&RFB
#2 ISE Realistic Colors
Easier AI for TMO 2.5 by Orpheus
EZ Plot V1.0