Complex sentence: The British allowed a corpse, disguised as a British officer, to drift ashore in Spain carrying a briefcase containing fake secret documents that supposedly revealed that the Allies were planning to invade Greece and Sardinia, and had no plans to invade Sicily.
Split into simpler sentences: The British allowed a corpse, disguised as a British officer, to drift ashore in Spain carrying a briefcase containing fake secret documents. The documents purported to reveal that the Allies were planning to invade Greece and Sardinia and had no plans to invade Sicily.