I'm confused as to why everybody is talking about selling funds. You can just do a direct transfer. Since the OP only holds Vanguard funds, Vanguard will accept them without having to liquidate them before the transfer.
The transfer has no tax consequences whatsoever. There may be an outgoing ACAT (transfer of funds) fee at USAA, but there is no receiving ACAT fee at Vanguard as far as I am aware.