Complex sentence: Project Catherine was the name of a proposed Baltic Sea offensive by the Royal Navy to be undertaken in the spring of 1940 whith the aim of interdicting German sea borne commerce with the Soviet Union, Finland, Sweden and the Baltic States.
Split into simpler sentences: Project Catherine was the name of a proposed Baltic Sea offensive by the Royal Navy to be undertaken in the spring of 1940. It aimed at interdicting German seaborne commerce with the Soviet Union, Finland, Sweden and the Baltic States.