But not generally by Americans. US rules for carrying classified material are stringent -- you don't stop on your route.In the UK there is a long and storied history of people leaving important briefcases/documents/computers on trains or in cabs or on the underground.
Of course, info like this wouldn't be couriered by an analyst for an informal exchange. That sort of data would be covered under the Five Eyes agreements and shared formally between the various agencies. And the US agency in question wouldn't be the CIA but the Office of Naval Intelligence, which has access to the technical experts to assess it properly.