possible deployment within 2 years...and he had obviously already begun prepping for his new career (in his case, politics)...as tens of thousands of other military personnel did during that time period. The request was approved by his superior officers...end of story...unless you choose to persist in inventing one.
Link: https://www.pbs.org/newshour/politics/fact-checking-attacks-on-walzs-military-record-by-vance-and-other-republicans