I suspect the fact that the most effective way of finding a target was to listen in on the enemy signals and then go wait for them to come to you went a long way toward slowing more complex hydrophone development in the U.S. Navy. For most of the war the American subs also had radar and the Japanese escorts, mostly, didn't, so running on the surface with the emitter going wasn't nearly as risky as it would have been in the Atlantic. After the war, when the "enemy" became a power we couldn't listen in on as easily, there were tremendous advances in passive sonar/hydrophone technology, ultimately leading to the massive phased array systems in modern boats. (Not to mention permanent hard-wired hydrophone arrays set up along the coasts and at natural choke points.)

The American JP hydrophone was a very simple device. Just a long iron bar with copper wire wrapped around it, and sound absorbing material covering the rear of the bar to make it directional. You plugged the coil into an outlet on the panel and ran a DC current through it, which magnetised the bar. This turned the whole thing into a great big microphone. (You had to remagnetise the unit frequently when under attack, since the concussion from the depth charges tended to demagnetise the bar -- a problem with most permanent magnets.) Then you shifted the plug to the amplifier input to listen. It was trained with a hand wheel, located in the forward torpedo room. It also used one of those old "magic eye" tubes you used to find in FM radios to fine-tune the bearing.

There were also two supersonic sonar head that could be extended out from the bottom of the hull. These were also mostly used passively, particularly to listen for enemy sonar. The equipment associated with these was located in the conning tower. Used on single-ping setting, this could be used to get a much more accurate range than was possible with the stadimeter in the periscope, which required knowing the exact masthead height for accuracy. You'd have three men on the sonar suite during an attack, two in the conning tower and one in the forward torpedo room.

J.T. McDaniel