Prince Adalbert was a naval officer serving on light cruisers in 1918. A light cruiser is a medium-sized general purpose warship above destroyers and below heavy cruisers and aircraft carriers in size. The Russian navy operates modern vessels comparable to what were called light cruisers, but Western navies do not (although the latest US Navy destroyers have the bulk and price tags of light cruisers). The German navy was largely bottled up in port at the time.
From eBay; removed monocolor tint and increased exposure and contrast. Also posted to Princess Adelaide of Saxe-Meiningen’s Subalbum here.