In 2012 the CIA produced a classified document, called Schengen Overview, which looks at travel controls within the Schengen area and discusses how these might affect ‘operational travelers’. Its objective is “to help US intelligence personnel protect their identities and operational activities while abroad.”
Having mentioned this document at a seminar this morning, I’ve put the reference here so I can find it again.
On the whole the CIA does not think that the Schengen system poses any threat to its activities: “Schengen border-check guidelines for third-country nationals suggest that additional information or suspicious activity would be required to expose alias identities of tradecraft-conscious operational travelers, even those subjected to more thorough secondary screening.” (This sentence is classed ‘Secret/ No foreign eyes’, for some reason.) Sadly there are no hot tips on how to get through passport control without a valid document, but it is interesting to see one government studying how to get round the rules set by another.