https://www.sfgate.com/news/article/Biden-deferred-disqualified-from-Vietnam-duty-3196927.php
According to the documents, Biden, 65, received several deferments while he was an undergraduate at the University of Delaware and later as a law student at Syracuse University. A month after undergoing a physical exam in 1968, Biden received a Selective Service classification of 1-Y, meaning he was available for service only in the event of national emergency.
"As a result of a physical exam on April 5, 1968, Joe Biden was classified 1-Y and disqualified from service because of asthma as a teenager," said David Wade, a campaign spokesman.
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According to records the Associated Press obtained from the National Archives, Biden registered Feb. 15, 1961, with the Selective Service, when he was an 18-year-old student at Archmere Academy in Wilmington, Del. The archives' documents do not include any information about his classification or physical exam.
Documents provided by the Obama campaign indicate Biden received a classification questionnaire in October 1963, when he was enrolled at the University of Delaware, and received his first 2-S student deferment a month later. Additional deferments were granted in roughly 12-month intervals, the last coming in January 1968.