Complex sentence: Just before the start of World War II "O 14" was in Curaçao, and because there was no need on the Allied side for a Dutch submarine "O 14" returned to Europe.
Split into simpler sentences: Just before the start of World War II "O 14" was in Curaçao. Because there was no need on the Allied side for a Dutch submarine to be stationed there, "O 14" returned to Europe.