Frank -
I agree the concept could only have been marginally successful -- assuming the net could reliably cause torpedo detonation at some distance from the hull, the shock wave from a detonation at that range would still be roughly equivalent to a depth charge or near miss aerial bomb with significant risk of hull damage.

Such nets were nonetheless deployed in significant quantities. Some were devised for use while the ship was underway, but the speed and maneuverability penalty was soon recognized as a major disadvantage to the ship\'s unencumbered ability to outmaneuver straight-run torpedoes.

Given the difficulties experienced in both Germany and the United States as a result of inadequate testing of torpedoes (generally attributed to the cost of torpedoes) it seems unlikely torpedo nets were ever subjected to meaningfully realistic tests. Japan seemed uniquely willing to extensively test torpedo designs between the world wars. (Who knows of torpedo net test data?)

In any event, the torpedo net concept seemed to fall out of favor between the wars as torpedoes were designed to explode beneath ships (and go under protective nets.) The large pre-war investment in protective net hardware, however, (like battleship armor) remained in evidence during the second world war (particularly in fixed harbor installations at greater distances from the ships being protected) as defensively minded individuals clung to the possibility that nets MIGHT help. =AL=