Complex sentence: In World War I Then Captain Greenslade received the Navy Distinguished Service Medal for his work during mine laying operations in the North Sea, and served throughout World War II, first as Commandant, Twelfth Naval District, and later as the Commander, Western Sea Frontier.
Split into simpler sentences: In World War I Then Captain Greenslade received the Navy Distinguished Service Medal for his work during mine laying operations in the North Sea. He held a couple different commands throughout World War II, first as Commandant, Twelfth Naval District, and later as the Commander, Western Sea Frontier.