Why the Brandenburg class mixed 11-inch gun lengths

Why did the Brandenburg class not carry six identical 11-inch/40 guns?

Ballistics, displacement, cost, and a design decision all contributed to the mixed-length main battery.

Using six identical long guns was not merely a ballistic question. Longer weapons affected the weight and space available within the design. Expense also constrained what could be installed across all three twin mountings. The mixed battery therefore reflects ballistics, displacement, cost, and a designer's preferred arrangement.