Why a 1930s German 210 mm cruiser gun would be a new design

Would 210 mm guns for an Admiral Hipper-class cruiser have to be newly designed?

Yes; the old 8.3-inch production tooling was gone by 1934, so Germany would need to recreate the industrial capability and develop a new weapon.

The question asks whether a 210 mm gun for the Admiral Hipper class could reuse an older German weapon. The panel says the First World War tooling and production capability were already gone by the time the ships were designed in 1934. Germany would therefore need a new gun and new manufacturing equipment even if it selected a familiar nominal caliber. Contemporary documents apparently considered a 210 mm cruiser, but the panel finds the choice puzzling when the internationally common 203 mm standard already existed. The exchange is interrupted by unrelated conversation before the answer returns to the lost production base.