Mods used: Background mod by Tully2001, FineTuner by HellFireKoder.

Info from WT wiki:
Work began on the concept of self-propelled anti-aircraft guns after Germany lost its foothold on air superiority to the Allies. The anti-aircraft vehicles would protect forward tank units from low-flying attack aircraft by being able to advance alongside them. The first few products of the "Flakpanzers" were the Wirbelwind and Ostwind built upon the Panzer IV hull. However, more protection was needed for the gun crew and an output in self-propelled anti-aircraft guns must be met to support all of their tank forces. Thus, the decision was made to use the Panther hull also employed in German service.
The Panther tank was developed upon for work, the project was designated the Coelian. The development tested various of armaments on the tank chassis, ranging from the 20 mm MG 151, the 3.7 cm FlaK 43, and a 5.5 cm gun. Development on the turret with the 5.5 cm gun began in May 1944 alongside another that mounted a dual-mounted 3.7 cm FlaK 43 instaed.

Despite the project's ongoing status, it was soon cancelled due to the more urgent need for tanks and diversion of resources to Germany's defenses. This was due to the Allied invasion in Normandy and the ensuing bombing campaigns launched. which severely impacted Germany's infrastructure. Thus, the Coelian project was cancelled from lack of resources, with only one wooden prototype of the 5.5 cm turret was produced in February 1945 atop a Panther D hull.