just a little off topic - today the postman brought me a new book to complete my naval libary: "Fischdampfer und Walfangboote im Krieg / Fishtrawler and whaling vessels at war - operation of 17th sub-hunting-flotilla in Norway"
but now back to our "problem"
... and to bring the discussion to an end - I found a very interesting pic of the famous "Raketenabschussgerät für Drahtseilraketen / rocketlauncher for wire-rope-rockets"
I think the shape of this device is very, very similar to that on HaJü's gunshield.
The author, a former commander of a sub-chaser writes, the smoke- and fire-trails of that rockets were clearly visible, but it would have been better to also have rockets with HE-warheads to fend such strafer attacks by lots of a/c off the norwegian coast.