Which of the following is not allowed when transmitting Secret material using aircraft?

The correct answer is that intermediate stops are not allowed when transmitting Secret material using aircraft. This restriction is due to the inherent risks involved with making stops during the transportation of classified material. Each intermediate stop increases the potential for interception, unauthorized access, or compromise of the sensitive information being transported.

In contrast, the use of military escorts is a common practice in securing and safeguarding classified material during transport, ensuring that there is a presence of trained personnel who can respond to any threats or incidents. Civilian pilots can be utilized in certain contexts, provided they have the appropriate clearances and follow stringent regulations for handling classified materials. Additionally, transporting Secret material via commercial airlines is permissible under specific guidelines, especially when the aircraft and personnel are cleared for such operations.