Modernising Schlesien for continued service

How would you modernize Schlesien to keep her viable?

Replace the machinery with small-tube boilers and standardize the secondary armament around dual-purpose guns rather than a mixed battery.

The proposed refit begins by replacing Schlesien's machinery with small-tube boilers, improving the usefulness of the old hull before adding weapons. The existing secondary battery would then be removed rather than preserving several different specialized mountings. As many dual-purpose guns as the ship could support would provide one coherent battery for surface and anti-aircraft defence. A mixed secondary armament can result when designers pursue an ideal gun for each separate task. A successful modernization starts by choosing a mission and simplifying the systems needed to perform it.