(The Germans were never able to dope out a
workable proximity fuze. Acoustic? Don't make me laugh!).

The Germans had every type of proximity fuse under development at the
end of the war including: radio, EM, IR, electo-optical, and your
favorite- acoustic! Ever heard of Kranich? The X-4 aam used it:

http://www.luft46.com/missile/x-4.html

Rob