The communication (COMM) mode is utilized for two-way underwater voice communication with other appropriately equipped aircraft, ships or submarines operating within range. Voice communication operation is activated by placing the MODE switch to COMM. Voice transmission is accomplished by use of position 3 on the radio transmitter selector panel from either the pilot, co-pilot, TACCO or SENSO/Sonar operators position. Volume of received communications is adjusted with the RAD VOL control on the radio transmitter selector panel. To adjust the AUDIO GAIN control on the sonar indicator, the SONO DIRECT switch on the Sonobuoy Receiver Control Panel shall be placed in the SONAR DIRECT position. When the AUDIO switch is set to ALL, reception of the underwater voice transmission is independent of cursor selection. Releasing the transmit switch permits monitoring voice signals from other similar underwater communication systems, if SONAR is selected on the radio receiver selector panel. However, if the AUDIO switch is set to ONE, reception of underwater voice signals can only be accomplished by placing the cursor circle in the CRT selector in which the noise spoke on the target bearing appears.