Incoming!

[Sailor Steve]

There has been talk on the SH4 boards about whether Japanese merchants had hydrophones, since some in real life did carry depth charges, and in that game they will suddenly start zig-zagging for no apparent reason.

Well, I just found out that some American merchants at least carried some form of passive device apparently referred to as a 'Torpedo Indicator'. A quick Google search turned up only active weapons indicators as used on warships for their own torpedoes, so I'm not sure how it works. I assume it's some form of passive omnidirectional hydrophone device that beeps or something when an incoming torpedo is detected. It doesn't seem to have worked particularly well in this case, but there it is.

At 00.08 hours on 2 Jul, 1943, the unescorted Bloody Marsh (Master Albert Harrison Barnes) was on her maiden voyage, when the ship´s torpedo indicator sounded after detecting the approach of a torpedo from U-66.

http://uboat.net/allies/merchants/2972.html