(1) The voltage of the 12-volt nickel-cad- 
mium battery under load. 
(2) The voltage of the 26-volt depth-cir- 
cuit battery. 
(3) The frequency and voltage level of the 
200-cps oscillator in the depth circuit. 
(4) The presence and level of the 13.5-ke 
carrier in the depth circuit. 
(5) The operating condition of the recorder 
and its four amplifiers. 
Test-unit information was obtained visually 
from the VU meter. A four-position selector 
switch and a visually monitored VU meter permit- 
ted reading the 12-volt, 200-cps and playback 
signal levels. The 12-volt, 26-volt, and 200-cps 
levels were put directly on the VU-meter termi- 
nals through an appropriate series resistance so 
that the meter read in decibels above or below 
the design level. 
With the VU-input selection switch in the 
"playback" position, the AP24 playback-amplifier 
output was monitored. The VU meter which indi- 
cated the recorded signal of all the channel 
signals combined or of channel 1, channel 2 
audio, or channel 2 FM alone was recorded. The 
desired signal was selected by properly setting 
a four-position "record monitoring" switch which 
controlled the B+ voltages to the amplifiers in 
channel 1, channel 2, and the depth circuit. 
This arrangement provided a separate visual in- 
dication of the recording of any signal on chan- 
nel 1 or channel 2 audio inputs or of the re- 
cording of depth-circuit signals. 
A "remove 200 cycles" button made it pos- 
sible to record the unmodulated 13.5-ke carrier 
signal on "channel 2 FM" and obtain a visual in- 
dication of the "clear" carrier recorded level 
on the VU meter. 
The hydrophone inputs were bypassed and had 
no connection to the electronic system during 
checkout. Prior to launching, the continuity of 
the complete system, from the hydrophones to the 
tape, was tested, 
The calibration precedure performed two im- 
portant functions. First, reference-signal lev- 
els at 1000 cps and 8000 cps were recorded on 
the tape by means of an oscillator wand and the 
proper attenuation pad. Second, a calibration 
of the depth-measuring circuit was made by feed- 
ing channel 2 FM of the tape a calibrating signal. 
19 
The insertion of the checkout unit into the 
electronic system replaced the pressure-trans- 
ducer potentiometer by the checkout unit's pres- 
sure-transducer-simulator potentiometer made up 
of precision resistors accurate to + 0.5 ohm. 
The simulator passed signal levels corresponding 
to actual pressures of 0, 15, 30, 37.5 and 45 psi 
used to modulate the 13.5-ke carrier. Each of 
the resulting FM signals was recorded during the 
checkout procedure by setting the record-monitor 
switch to "channel 2 FM," the VU-meter monitor 
switch to "playback," turning on the recorder, 
and setting the simulator to various pressure 
levels by hand. 
The record-level calibration signals with 
which to compare hydrodynamic-flow-noise data 
were recorded during the checkout procedure by 
inserting the oscillator wand (a small battery- 
powered oscillator for field use) connected to 
an attenuation pad into the channel 1 and channel 
2 checkout-unit inputs. The wand and pad fed to 
the recorder amplifiers reference signals of -75 
db on a l-volt reference at 1000 and 8000 eps. 
Only the 1000-cps signal was recorded for channel 
2 audio because of the 6000-cps cut-off of the 
audio portion of this channel. By comparing the 
hydrodynamic-flow-noise level to these signal 
levels on the tape, an accurate value of the 
hydrodynamic-flow-noise level was obtained. 
Launching and Recovery Procedure 
Preceding the actual drop, the missile mid- 
section was mounted horizontally in the launch- 
ing frame (Fig. 2) and the electronics partially 
inserted by sliding the electronics rack along 
the tracks mounted inside the missile midsection. 
The checkout procedure and calibration already 
described were then performed, the installation 
of the electronics rack was completed, and the 
missile was rotated to a vertical attitude in the 
launching frame. The missile nose section was 
threaded onto the midsection and the tail mounted 
and locked by means of a hydraulic jack located 
at the top of the launch frame. The jack loaded 
the release spring by forcing down a long steel 
rod which slides down the middle of the tail and 
fits over the support rod mentioned previously. 
The missile completely assembled, was held in the 
launch frame as shown in Fig. 1. The launch 
frame and missile assembly were lowered through 
the center of the launching platform by means of 
a winch and steel cable until the upper end of 
the launch frame was just below the surface of 
the water. 
The missile was released on opening the 
