The German proximity fuse.

You'll find that there were at least two other allied photoelectric
based fuses. The first one entered service on rockets (it couldn't
handle the shock of a gun launch) but its photocells found application
in the punched paper tape reader of the colossus machine used in
decrypting Enigma. The second system could withstand a cannon lauch
and entered service. It used a torrodial perspex lens around the
circumference or rim of the shell that focused on a photocell.

To be fair most of these German fuses were for different purposes than
cannon shell launch. Missiles need more sophisticated and jam
resistent radio proximity fuses. In addition the Germans were clearly
hedging their bets by developing a spread of systems to reduce their
exposure to Allied Jamming attempts. The German were big investors in
both passive and active infrared technology and this was begining to
pay of in 1945.

In part the plethora of projects represents the secrecy
compartmentalisation, as well as intersevice rivalries but also a
policy of phased development was in place so that the Germans could
catch up and stay ahead in areas such as radar.

In reality relying on one proximity fuze type is a recipe for disaster.
The allies relied on secrecy and then the hope that the Germans
couldn't react in time.

The Wasserfall and Enzian Surface to Air missiles for instance had a
spread of guidence and proximity fuze systems under development.
Wasserfall had a 3 axis gyroscopic version of the two axis gyroscopic
guidence system in the V2 including apparently the PIGA accelerometer.
Even without external guidence it would have placed itself within a few
hundred meters of its target. There an infrared terminal homing system
was to be used (Madrid), or alternatively command guidence using a
radar called "Mannheim" (80 of these track-lock entered service) or
visual command guidence. There was also a semi active guidence system
under development called "Moritz". The command link was based on a
specially developed version of the "Khel/Strassbourg" system used on
Fritiz-X and Hs 293 but also on a purpose built system called
"Kogge/Brigge"

The smaller Ruhrstahl X-4 wire guided Air to Air missile opperated with
basic wire guidence and a contact fuse backed up accoustic proximity
fuse called "Kranich". A accoustic terminal homing system "Dogge" was
also under development as was an infrared terminal homing system and
proxitmity fuse. The same systems were planed for the Enzian missile
including an accoustic homing head called "Archimedes"

The accoustic homing systems worked quite well. A Me 262 Jet equiped
with accoustic homing systems could detect a bomber and its directions
to about 4-5 miles range.

There were 5 quite effective surface to air missiles bodies were
developed:
Wasserfall, Enzian, Hs-117, Rheintochter R1.and R3 but non received the
focus they needed to enter service. To one degree or another they
suffered manpower shortages or sabotage.