C - Foreign National In Transit
The C nonimmigrant visa category is reserved for nonimmigrants who are in "immediate and continuous transit" through the United States. Such immediate and continuous transit may be for:
(1) crewmen who are coming to the United States to join vessels or an aircraft (these individuals may be issued C and D visas concurrently depending upon the circumstances);
(2) persons covered under the United Nations Headquarters Agreement (individuals who are performing services for the United Nations or an ancillary agency of the United Nations).
The C nonimmigrant visa category may be granted to a foreign national for "immediate and continuous transit" for a period of time that is not in excess of twenty-nine (29) days. The C nonimmigrant visa category is not likely to be one that is often encountered.
The regulations for this nonimmigrant visa category can be found at 8 CFR Sec. 214.2(c).