Click on the “Government Account” link at the bottom of the http://vanguardmil.com home page, then the “Click Here” link. Or, actually here’s the direct URL:
And, then it should be clear: check “Apply for a … Sea Cadet Unit account…”, and select the “Sea Cadet Unit” radio button. You’ll be prompted for our Unit Code which is: 042TAY
When I did this I got an error because the email address I signed up here was already in use because I had an existing account since I had ordered before – I ended up calling the Vanguard East phone # at the bottom of the page and they added the code.