Complex sentence: Ships of the class spent their Italian career in colonial duty, like "Lepanto" in China; in 1937 "Milazzo" and "Dardanelli" were sold to Bolivarian Armada of Venezuela in change of a great amount of naphtha for boilers.
Split into simpler sentences: Ships of the class spent their Italian career on colonial duty, with "Lepanto" deployed to China. In 1937 "Milazzo" and "Dardanelli" were sold to the Venezuelan Navy in exchange of a great amount of naphtha for boilers.