Sentence:  The big air raids ... were much more dreadful than the air raids of the World War. They began with a nightmare of warning <WSD>maroons</WSD>, sirens, hooters and the shrill whistles of cyclist scouts, then swarms of frantic people running to and fro ... 
Meaning of the word marked with <WSD> tags:  A rocket-propelled firework or skyrocket, often one used as a signal (e.g. to summon the crew of a lifeboat or warn of an air raid).