C-3 transit visa allows accredited foreign government officials to enter into the US while in transit to another foreign country for official work. Each person including immediate family members (even children and babies listed in parents' passports), attendants, servants and personal employees of the official needs to apply for a separate C-3 transit visa.

An immigration officer at the port of entry can admit a person holding a C-3 transit visa for the duration determined by him/her, but for a maximum duration of 29 days. You must leave the US on the proposed flight or ship of departure, or within 29 days, whichever is earlier. You must pass in immediate and continuous transit through the US.

Following documents are required for C-3 transit visa:

• Passport
  
  
• One photograph
  
  
• DS-156, nonimmigrant visa application form.
  
  
• DS-157, supplemental nonimmigrant visa application form.
  
  
• Proof of permission to enter the country of your final destination such as passport with a valid visa, or evidence that a visa is not required.
  
  
• A common carrier (flight or ship) ticket or other proof of transportation arrangement to final destination.
  
  
• Financial documents to show that you have adequate funds to cover the cost of your transit journey.
  
  
• Consular officer may ask for additional documents to verify the actual purpose of applying for a transit visa such as the position on which you are traveling, the purpose of the visit etc. It is not possible to predict the exact documents that may be asked.

You must apply for C-1 transit visa at the nearest US embassy or consulate. All applicants over 14 years to 79 years of age must apply in person and must schedule an appointment before visiting the US embassy or consulate. Applicants under the age of 14 and those 80 years and above may apply for a transit visa by mail.

Application procedures vary depending upon the consulates in different countries. If you are applying for a transit visa in India, you can find detailed application procedure. Processing times can vary a lot in different countries and there are delays of several months in places like India before you can get the visa appointment. It is wise to plan very early because of constant heavy demand for US visas.