Pussycat escorts

[SSI01]

I've run into an interesting situation in SH4 others may have encountered. If you've had a rough patrol and then run into this situation you may not want to complain, it could be a badly-needed break.

After landing an agent at Dalian, China I have been ordered to proceed to the E. China Sea and engage enemy merchant shipping. In the northern reaches of the ECS, just south of the Korea Strait, I detected and reported an enemy convoy w/escorts. COMSUBPAC msgs back saying escorts are priority targets and I should engage. OK, evaded initial detection, went deep, and broke toward convoy. Used convoy noise to mask approach as much as possible. Went to periscope depth and fired torpedoes at two merchies thinking this would draw DDs toward me. Sank one, damaged the other. Amazingly not one of the three Japanese DDs (can't remember type, don't have game open right now) showed the least bit of aggressiveness and searched for my boat on outskirts of convoy. Even putting boat (Porpoise) at 35 feet to expose shears didn't result in them becoming apoplectic and charging down my scope.

Time is February 1942. I don't have realism settings set very high, I'm afraid. Although, in the past this made absolutely no difference, they would do their best to rattle the crew's eyeteeth with DCs. Any idea(s) for the lack of aggressiveness?