I found a site that details out the inter-war efforts in Accoustic Location and Sound Mirrors - it's a brief site, but has some interesting pictures and information detailing the efforts of:
the U.S.A....
...the British...
...the Germans...
... the Japanese....
... and the French....
and he briefly touches on Sound Mirrors...
... it's pretty interesting stuff on a little known (or discussed, anyway) technology that was quickly supplanted by the more accurate and longer range radar.
Also, according to this site, the first Japanese attack on the fortress island of Corregidor (in the Phillipines) on 29th December 1941 was detected by American acoustic locators.
.... oh, yeah..... here's the link
Acoustic Location and Sound Mirrors.
-whatever
-Lou