15 cm Kanone 16

7.7 cm FK 96

Skoda 305 mm Model 1911

can we get the panther turret like the t-54 turret

I have many suggestions so I'll list them in one post.
M4 Sherman(75mm and 105mm)
M4A2(76mm)
M4A3(76mm more durable than A2)
M-51(105mm)
Pz4J(75mm)
Pz4H(75mm more durable than J)
Tiger 1
Tiger 2
and PantherD

I'll toss a few ideas out there.

CRAM 30mm, could also have artillery interception like the lasers from rim atomics
Patriot missile 4 pack
Bushmaster mk 38 25mm, LAV or Bradley turret, or the naval standalone
M 51 quad .50, on either it's cute little 2 wheel trailer or the static base plate

I have no idea if it's size would be viable for Rimworld but I would be interested to see Yamato's 460mm guns added.

https://www.naval-encyclopedia.com/ww2/japan/yamato

16-inch/50-caliber Mark 7 gun plz

I just had an idea, Gustav, for when Karl simply isnt big enough. XD

Autocannons
the Phalanx CIWS - uses 20*102mm - https://en.wikipedia.org/wiki/Phalanx_CIWS
the Goalkeeper CIWS - uses 30×173mm - https://en.wikipedia.org/wiki/Goalkeeper_CIWS
the Dardi - uses some type of 40mm - https://en.wikipedia.org/wiki/DARDO
defiantly all autoturrets

if you want something lower tech
Bofors 40mm anti air gun - ammunition varies by model, but all 40mm https://en.wikipedia.org/wiki/Bofors_40_mm_gun

personally I prefer the Dardi, because 736 40mm HE rounds at 300 RPM (or 450 in the updated version) is a good way to say '♥♥♥♥ off" also the additional 200 APFSDS rounds for the updated version is a nice addition for when you are playing with the armored centipedes addon.

@Acerrrr12, bofors is already in the mod, DCA 40's 40 mm Mle 51 T1 is basicly french version of 40mm Bofors L/70.
the M247 also uses Bofors L/70 but more modern ammunitions.

rotary gun CIWS are gonna mess up with the game's tick rate because of the fire rate, but DARDO CIWS looks doable.

Sorry for not looking close enough (I posted that a bit before midnight on my end), also I don't really know whats equivalent to what when it comes to naval guns.
And for a workaround you could have a (base game rimworld) shotgun style projectile for the CIWS where it's just a bunch of pellets (or in this case rather large bullets) counted as a single projectile which should simplify the processing a great deal. anyway i'm off to bed it's 4:53 AM on my end.

Oerlikon Skyranger 35 - uses 35 x 228 mm
Rate of fire: 1000 rounds/min
https://www.youtube.com/watch?v=Kb1FA12q6_w&list=PLlBo0IQ0E-_qhoeekQDLrCmhqBYr-mSZi&index=42

Please can you add LeFH 18s 105mm and sFH 18s 150mm or US M1 105mm and M2 155mm Long Tom

Kirov Battlecruiser's dual barrel 130mm gun....
203mm malka/pion