Which combination of procedure words should never be used together in military communication?

The combination of "Over and Out" should never be used together in military communication because of the specific meanings assigned to each term. In military radio communication, the term "Over" indicates that the speaker has finished their transmission and is awaiting a response from the recipient. Conversely, "Out" indicates that the speaker has finished communicating and does not expect a reply. Using both terms together creates confusion about whether a response is required, as one suggests waiting for an answer while the other indicates the conversation is concluded. Clear communication is vital in military operations, so adhering to established terms helps prevent misunderstandings.