What Mode 1 squawk should be used when desiring a tanker to join?

When a tanker is to join another aircraft or a formation, the standard Mode 1 squawk used is 70. This specific squawk code is designated for tanker operations within military air traffic control. It helps ensure that both the tanker and the receiving aircraft are communicating on the same frequency and operating under a predefined identification code, facilitating coordination and safety during the joining process.

Squawking 70 provides clear identification to air traffic control, which is critical in maintaining situational awareness, especially in environments with multiple aircraft operating in close proximity. This allows controllers to track the movement of the tanker and its associated aircraft effectively.

Other squawk codes like 71, 72, and 73 are associated with different operations or designations and are not the standard for tankers to join. By using squawk 70, the crew acknowledges and adheres to established protocols, thereby ensuring operational efficiency and safety in the airspace.