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The R. VI was the first of the Siemens-Schuckert R-type aircraft to reach service , and between July 1916 and November 1917 saw service on the Eastern Front before it was declared obsolete and dismantled .
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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:
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