Complex sentence: Four boats were transferred to the Spanish Republican Navy during the Spanish Civil War, two continue in service after the war in Spanish navy to 1946 and a number were transferred to North Korea after the end of the war.
Split into simpler sentences: Four boats were transferred to the Spanish Republican Navy during the Spanish Civil War, two continue in service after the war in the Spanish navy until 1946. A number were transferred to North Korea after the end of the war.