7. OPERATION OF INTERPHONE AND RADIO. a. Interphone communication is provided for each crew member, and radio communication is provided for the commander and the assistant driver, who is also the radio operator. The interphone is used whenever the tank destroyer is operated. After mounting, headsets and microphones are put on and tested according to the following procedure:

(1) Each crew member plugs in his headset and microphone cords.

(2) The destroyer commander and assistant driver turn their radio-interphone switch to INT, and the other crew members to RADIO. The commander orders CHECK INTERPHONE. Each member of the crew reports "Ready" to the destroyer commander in the following order: gunner, assistant gunner, assistant driver, and driver. During this procedure, each crew member adjusts the volume control on his interphone control box to the desired level. Care must be taken that the microphone switch does not remain in a locked position.

(3) The RADIO-INT switches on all control boxes, except the destroyer commander's and the assistant driver's, must be set on RADIO. This is the normal position for interphone operation. Except in an emergency, no one but these two members may operate the RADIO-INT switch on his control box. In an emergency, the driver may signal the radio operator by throwing his control box switch to INT and simultaneously operating his microphone switch. He should immediately return his control box switch to RADIO. This signal consists of a loud tone in the destroyer commander's or assistant driver's headset which interferes with his reception of the radio. Upon receipt of this signal the commander, or assistant driver, operates his control box switch to INT at the earliest opportunity and establishes interphone communication with the crew. Whenever the commander must establish interphone communication with the crew, the assistant driver throws his switch to RADIO and tends the radio.

(4) The commander or assistant driver reports into the radio net at the designated time. When the net is opened, one qualified crew member must tend the radio at all times.

b. It is the duty of each man to check his personal interphone equipment upon mounting the destroyer; he should see that it is properly maintained, and report any difficulties to the destroyer commander.

c. Definite vehicle control commands and terminology reduce conversation to a minimum. The use of general conversation minimizes the value of the interphone, is conducive to frequent misunderstandings and disorder, and breaks down crew discipline. The following interphone language illustrates the simplicity and brevity which must be used:

(1) Terms.

(2) Commands for movement of destroyer.

(3) Commands for control of turret.

(4) Miscellaneous.