Complex sentence: He is chiefly known for commanding the 1st light cruiser Squadron operating in the Baltic Sea in 1919/20 which kept the sea lanes open to the newly independent Baltic States, enabling them to secure their freedom.
Split into simpler sentences: He is chiefly known for commanding the 1st light cruiser Squadron operating in the Baltic Sea in 1919/20. The squadron kept the sea lanes open to the newly independent Baltic States, enabling them to secure their freedom.