Aircraft Detection Before Radar

Aircraft Detection Before Radar....

I bet none of you ever saw this stuff before.

How air attacks were detected before radar...Old time acoustic hearing aids.

http://us.mc1108.mail.yahoo.com/mc/welcome?.tm=1324504059#_pg=showMessage;_ylc=X3oDMTBucmhobGR0BF9TAzM5ODMwMTAyNwRhYwNkZWxNc2dz&mid=2_0_0_1_12866452_AOANw0MAABKSUBGEtwfEPEz3B9A&fid=Inbox&sort=date&order=down&startMid=0&filterBy=&.rand=350727611&hash=165ab039f3688f30982af841c37b2560&.jsrand=5596872