The site can't be opened currently using general public security infrastructure. https://www.defensetravel.osd.mil/ "Peer’s Certificate issuer is not recognized." The certificate chain is not trusted, presumably because part of it is missing; or it only relies on the path shown in the attachment (DoD– or Grumman–supplied corporate trust roots.) See https://www.ssllabs.com/ssltest/analyze.html?d=www.defensetravel.osd.mil for analysis. ''(If this is not error on their side and is expected, you might have been given instructions how to load the corporate certs, or might have been instructed to add these certificates as an exclusion.)''