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Due to ordnance supply problems , the site instead consisted of three 210-mm navy guns , with only two of them protected by large concrete casemates , a command post , shelters for personnel and ammunition , and several defensive machine-gun emplacements .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None