instance, does not want the cabin blasted with calls for
individuals to lay down to the spud locker. The BM of
the watch is responsible for passing the word; but if he
or she is absent and you are required to pass the word
by yourself, be sure you know which circuits should be
left open, Some parts of the ship have independent MC
circuits of their own, such as the engineers' announcing
system (2MC) and the hangar deck announcing system
The bull horn (6MC) is the intership announcing
system, but it seldom is used for actual communication
between vessels. It is, however, a convenient means for
passing orders to boats and tugs alongside or to
line-handling parties beyond the range of the speaking
trumpet. If the transmitter switch is located on the 1MC
control panel, you must be careful to avoid accidentally
cutting in the bull horn when you are passing a routine
word. The 1MC, 2MC, 3MC, and 6MC are all one-way
Such MC circuits as the 21MC, familiarly known as
squawk boxes, differ from the preceding PA systems in
that they provide means for two-way communications.
Each unit has a number of selector switches. To talk to
one or more stations, you need only throw the proper
switches and operate the press-to-talk button. A red
signal light mounted above each selector switch shows
whether the station called is busy. If it is busy, the light
flashes; if it burns with a steady light, you know that the
station is ready to receive.
Following is an example of how to operate the
intercom. You are on the signal bridge, at the 24MC
transmitter (fig. 2-19), and you want to call conn. First
you push the selector button marked CONN. We will
assume the line is clear for your message, which means
that a steady red light appears over the SIGNAL
BRIDGE selector switch at the conn transmitter. When
the operator at conn pushes on the SIGNAL BRIDGE
button, the signal lights at both stations begin to flash.
Now you can operate the PRESS-TO-TALK button and
start your message. Any other station attempting to cut
in gets the flashing busy signal.
The chief disadvantage of the intercom is that it
raises the noise level in any space in which it is used.
For this reason, it seldom is used when telephones are
manned. Intercom circuits that may be located on the
bridge are identified briefly as follows:
The 20MC, combat information announcing
system, connecting the same stations as the 1JS
Figure 2-19. Typical MC unit.