I ended up in a weird little rabbithole while looking into Unrotated Projectile launchers, and came across some very niche concepts/designs for handheld AA weapons for the British and the Japanese. And well felt inspired to share, since it would be a shame for the Germans to hog all the attention with the Luftfaust.
Japanese design
The Japanese design I came across was merely named the “AA Mine Discharger” or “阻塞弾発射機”
It should be mentioned that it could also be fired from the Type 11 70mm mortar.
So really the AA weapon in question should be considered the Shell/Aerial Mine rather than the launcher.
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It would be launched approximately 900-1200m before falling back down and the parachute would open at at 600m. From there 7 small bomblets/mines would be released, in effect either hitting an aircraft or acting as a rudimentary form of cluster munition.
Historically it would be produced between 1940 and 1942 though its disputed if they ever saw combat, however there is at least one story of IJN personally downing aircraft with it during an air raid, however the source for that last part isnt the most reliable.
In game I believe it could be a fun gimmick weapon, I doubt it would be very effective at all, either in its intended AA role or its secondary cluster munition role, so Im not worried about it being OP.
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British Design
As for the British design, The Holman Projector, has more concrete information available to it, though it was only handheld in practice, or in emergency, commonly instead it was mounted fully. Saying that it absolutely could and is certainly quoted to have been used as a handheld device.
The original prototype version pictured here.
The Holman Projector was a unique weapon of the war, being a pneumatic weapon and later a steam weapon, commonly fitted or equipped to ships though there were land batteries too. Personally in game I would like to see this arrive in the form of an engineer squad with a unique buildable object. Able to double as a mortar or AA weapon, since its a time fused weapon, it would be suitable for it to act as an air burst weapon in game, though in a more direct fire role.
There was also the Mk3 which was a semi automatic version, being loaded sequentially into the barrel. And order for 1000 of the Mk3 models were places, though the Mk4 version never left the drawing board, otherwise combined approximately 4500 such devices were created and used. Only 2 surviving to this day.
It is confirmed to have downed approximately 12 aircraft in its first year of use, however saw much more success deterring aircraft forcing them to attack from further away or in some cases even convincing the pilots to fully abort their attacks.
I was going to originally going to post this to suggestions, but instead of jamming it with stuff that will never be added, I thought Id just share it via the mess hall.