8-24 Change A
U.S. Navy Diving ManualVolume 2
The approved Navy diver communication system is compatible with the MK 21
MOD 1 and the MK 20 MOD 0. This is a surface/underwater system that allows
conference communications between the tender and up to three divers. It incorpo-
rates voice correction circuitry that compensates for the distortion caused by
divers speaking in a helium-oxygen atmosphere.
The divers voices are continuously monitored on the surface. All communications
controls are located at the surface. The topside supervisor speaks with any or all of
the divers by exercising the controls on the front panel. It is necessary for a phone
talker to monitor and control the underwater communications system at all times.
Line-Pull Signals. A line-pull signal consists of one pull or a series of sharp, dis-
tinct pulls on the umbilical that are strong enough to be felt by the diver (Figure
8-11). All slack must be taken out of the umbilical before the signal is given.
The line-pull signal code (Table 8-3) has been established through many years of
experience. Standard signals are applicable to all diving operations; special signals
may be arranged between the divers and Diving Supervisor to meet particular mis-
sion requirements. Most signals are acknowledged as soon as they are received.
This acknowledgment consists of replying with the same signal. If a signal is not
properly returned by the diver, the surface signal is sent again. A continued ab-
sence of confirmation is assumed to mean one of three things: the line has become
fouled, there is too much slack in the line, or the diver is in trouble.
If communications are lost, the Div-
ing Supervisor must be notified
immediately and steps taken to
identify the problem. The situation
is treated as an emergency (see
There are three line-pull signals that
are not answered immediately. Two
of these, from diver to tender, are
Haul me up and Haul me up im-
mediately. Acknowledgment con-
sists of initiation of the action. The
other signal, from the tender to
diver, is Come up. This signal is
not acknowledged until the diver is
ready to leave the bottom. If for
some reason the diver cannot re-
spond to the order, the diver must
communicate the reason via the
voice intercom system or through
the line-pull signal meaning I un-
derstand, followed (if necessary)
by an appropriate emergency signal.
Figure 8-11. Communicating with Line-Pull