Improving Bismarck with a dual-purpose secondary battery

What changes would most improve Bismarck?

Fit an effective dual-purpose secondary gun and avoid prolonged capital-ship engagements that risk damaging an isolated raider.

A good dual-purpose gun is the principal proposed improvement to Bismarck's separate specialised weapons. Such a battery would help in the different situations the ship could encounter. Remaining in combat with enemy capital ships is also questioned. An isolated raider needs to avoid damage that undermines its ability to continue the mission or escape.