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In 1947 , he was called up for national service in the Royal Navy and spent two years stationed in North Wales and the Firth of Forth .
 Royal Navy, North Wales, Firth of Forth
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Royal Navy, North Wales, Firth of Forth