Sentence:  Cuban S. S. R. : Whatever may have been the setbacks resulting from the unsuccessful attempt of the Cuban rebels to establish a beachhead on the Castro held mainland last week , there was at least one positive <WSD>benefit</WSD> , and that was the clear-cut revelation to the whole world of the complete conversion of Cuba into a Russian dominated military base . 
Meaning of the word marked with <WSD> tags:  something that aids or promotes well-being