18A1. General. A submarine, when on the
surface, must be in readiness to dive at any
time. This requires the vessel to be maintained constantly in diving trim so that little
or no trim adjustment is necessary after
submergence. The ship is rigged for dive
immediately after getting underway, in strict
conformance with the check-off list posted in
18A2. Types of dives . Three types of dives
are possible: 1) the quick dive, 2) the running dive, and 3) the stationary dive, the
choice being dictated by existing conditions.
In all dives the ship is placed in the condition
of neutral or negative buoyancy; the use of
negative buoyancy shortens the diving time.
A quick dive is made when the ship is
underway on one or more main engines. The
bow planers are placed on FULL DIVE and
the forward speed results in a maximum
downward thrust on the bow planes. As the
submarine submerges, the upper surfaces of
the hull and superstructure act as planing
surfaces and increase the downward thrust.
The quick dive is the fastest of the three
types and is used in acceptance trials of new
submarines, when it must be executed within
60 seconds from standard diving trim.
A running dive is performed in the same
manner in a minimum time, the only difference being that surface propulsion, at the
beginning of the dive, is by battery-powered
A stationary dive is made when the ship
is dead in the water. The main ballast tanks
are completely flooded and enough water is
flooded into the variable ballast tanks to destroy the remaining positive buoyancy.
Flooding and pumping may be alternated to
maintain the ship on an even keel at any
desired depth. This type of dive is sometimes
used during builder's trials to test and inspect the hull at various submerged depths
down to final test depth.
18A3. Control station. The necessary instruments and equipment for submergence and
control of the boat while submerged are
located in the control room. The control room
is the station of the diving officer who issues
the necessary orders during a dive and directs the men at the manifolds, pumps, and
diving gear in maintaining the submarine at
the desired depth. An illustration of the
control station is shown in Figure 14-1.
The control station includes the bow and
stern planesmen's stations and is equipped as
a. Depth gage, reading from 0 to 165
feet, indicates the keel depth,
b. Inclinometers indicate the angle of
the vessel's longitudinal axis with the horizontal.
c. The plane angle indicators are miniature diving planes, the trailing edges of
which range over degree scales and indicate
the angle of rise or dive on the bow and stern
d. A motor control contact-type switch.
provides selection of direction of rotation of
plane-tilting motor in those installations
using electrically operated planes. Hydraulically operated planes are controlled by a
e. The selector switch provides a choice
of motors on which the controller is to be
used. The bow planes may be rigged or tilted
according to the position of the switch handle. A similar device at the stern plane controller provides for use at the stern plane
motor to operate the after capstan.
f. The hand-operated clutch, on electric
drive, permits shifting from power to brand
operation of planes. Hydraulically operated
planes are controlled by a valve which, when
placed in the neutral position, permits manual drive direct to the planes.
g. A depth gage reading from 0 to 600
feet, mounted at the center of the control
panel, is visible both to planesmen and the
h. The rudder angle indicator, graduated in degrees, indicates the amount of left
or right rudder on the ship.
i. The aneroid barometer indicates the
air pressure in the ship.
j. The hull opening indicator light
panel, commonly referred to as the Christmas
tree (Figure 18-1), indicates the condition
of hull openings, vents and flood valves. Electrical contacts at these various openings and
valves operate red and green lights in the
panel. A green board shows that all hull
openings are closed.
18A4. Rig for dive . Before an actual dive
is undertaken, the submarine must be fully
prepared. Compensation must have been
made for all changes in weight since the last
dive, and all hull openings, except those necessary for the operation of the ship on the
surface, must be closed. The hull openings
not closed, and the reasons therefore, are as
a. Conning tower hatch which provides
passage to or from the bridge.
b. The hull ventilation supply valve
which remains open to permit the circulation
of fresh air.
c. The main engine induction outboard
valve which admits air to the engines.
d. The forward and after engine room
induction hull flappers which admit air to
both forward and after engine rooms.
The safety and negative tanks are flooded and the flood valves left open. All bulkhead watertight doors and bulkhead flappers
are checked for free operation. Outboard
battery ventilation exhaust valves, if installed, are closed and checked by sighting
the valve disc and by checking the mechanical indicator. Sufficient high pressure air, at
least 45 percent of total capacity, must be
cut into the manifold. Rapid and efficient
communication must be established between
the diving officer and all compartments.
All of these details must be checked by
one or more officers. When the diving officer
is informed that all preparations are completed, he reports to the commanding officer,
"Ship rigged for dive."
18A5. Diving procedure . Each ship has a
diving procedure which has been established
by careful consideration of its particular
characteristics, and is recorded in the Ship's
Organization Book of that submarine.
The diving signal is two short blasts on
the diving alarm, the second blast being the
signal to start the dive. Two blasts are used
Figure 18-1. The hull opening indicator light panel.
to guard against diving on an accidental
single blast. An alternate diving signal is the
word "Dive, Dive" passed orally.
When the diving alarm is given, the following procedure is observed (items marked
with all asterisk are executed at once without
*a. Stop all engines, shift to battery,
set annunciators on "All ahead standard,"
open engine room doors and air locks.
*b. Close outboard and inboard engine
exhaust valves, close hull ventilation supply
and exhaust valves, close inboard engine air
induction flappers, and close conning tower
*c. Open bow buoyancy vents and all
main ballast tank vents, except the group
or tank designated to be kept closed until
pressure in the ship indicates that all hull
openings have been closed.
*d. Rig out bow planes and place on
FULL DIVE. Use stern planes to control the
angle on the ship.
*e. Diving officer checks hull opening
indicator light panel for condition of hull
openings. Air is bled into the ship when
green lights show all hull openings closed.
Watertight integrity is assured when the internal air pressure remains constant.
f. The following operations are performed by direction of the diving officer, who
is guided by the existing conditions:
1. At 45 feet, shut the vents and slow
to 2/3 speed.
2. At 15 feet short of desired depth,
blow negative tank, shut its flood valve, and
vent the tank.
3. Level off at specified depth, slow to
1/3 speed, cycle the vents, and adjust fore-and-aft trim and over-all weight.
4. Diving officer reports to conning
officer when trim is satisfactory.
When diving in a heavy sea, the maneuver is accomplished most expeditiously by
diving with the sea abaft the beam.
B. SUBMERGED OPERATION
18B1. General principles . Submerged operation involves control of the submarine in both
the horizontal and vertical planes. Maneuvers
in a horizontal plane are controlled by the
rudder which functions in the same manner
as when on the surface. Control in a vertical
plane is achieved by varying the angles of
the diving planes and the submarine, combined with an adjustment of ballast to attain
the necessary state of buoyancy.
Submerged operations are usually carried on with the submarine in the state of
neutral buoyancy. Shortly before reaching
the desired depth when diving, the negative
tank is blown. This places the ship in the
state of neutral buoyancy in which the downward force of gravity is exactly- balanced by
the opposite force of buoyancy and the ship
will maintain its depth unless acted upon by
some unbalancing force. The state of exact
neutral buoyancy is probably never attained,
but the approximation is near enough to
allow depth control to be exercised easily by
the diving officer.
In all normal submerged operations, the
submarine is underway at relatively slow
speeds. This horizontal motion through the
water enables the surfaces of the diving
planes to correct the effect of any slight positive or negative buoyancy and also to increase or decrease the submerged depth at
the order from the conning officer. The effect
of the diving planes is proportional to the
speed, and the speed at which the depth can be changed increases with the inclination of
the submarine's longitudinal axis from the
horizontal. When the axis is inclined, the hull
presents planing surfaces. The resultant upward or downward thrust is added to that of
the diving planes.
In Chapter 2, final trim is defined as the
adjustment of ballast while submerged which
maintains the submarine at the desired
depth, on an even keel, at slow speed, with a
minimum use of the diving planes. The diagram in Figure 18-2 represents a typical
submarine submerged and in final trim. The
forward moments due to gravity, FGM, are
exactly equal to the opposing moments, FBM
due to buoyancy. Also the after moments,
AGM and ABM, are equal. To meet the conditions of stable equilibrium, the forward
Figure 18-2. Forces affecting depth control.
moments must equal the after moments and
the center of gravity must be below the
center of buoyancy and in the same vertical
When forward motion is imparted to the
submarine, new forces, due to the unsymmetrical contour, come into play and disturb
the static equilibrium. These forces are
indicated in the diagram. The upsweep
of the forward end presents a planing surface, the resultant effect increasing with the
speed. The superstructure, conning tower
fairwater, periscopes, masts, deck guns, and
other objects present more or less vertical
surface above the center of buoyancy. The
tendency of these forces is to rotate the submarine about a center with the result that,
as speed is increased, the submarine tends to
assume a small up-angle and decrease its
This rotational tendency is counteracted
by the diving planes. Since the location of
the planes is not symmetrical about the center of buoyancy nor about the longitudinal
axis of the submarine, the effect of the bow
planes on the movement of the vessel is quite
different from that of the stern planes.
The location of the planes is shown in
Figure 18-2. (The dimensions shown are
approximate, and apply only to the submarine described herein.) As indicated, the bow
planes tend to change the vertical position
of the submarine on an even keel. There is a
certain rotational moment, but it is counteracted to a great extent by the longer after body which acts somewhat as a stabilizing
rudder, resisting angular displacement.
The stern planes are located at a greater
distance from the center of buoyancy and, although they are smaller in area, their effect
is much greater than that of the bow planes.
Their effectiveness is increased by their location directly aft of the propellers. This combination of a long moment arm and location
in the propeller wash results in a rotational
movement. Thus the bow planes are normally used to control the depth, and the stern
planes the angle of the ship.
From the time the dive is started until
the submarine reaches the specified depth and
is placed in final trim, the diving officer may
have control of the speed. It is important,
therefore, that the various necessary operations be completed in the minimum time so
that speed control may be returned to the
18B2. Trim analysis . To place the submarine
in final trim the shortest possible time
requires a swift, accurate analysis of the
submarine's condition. This analysis may be
made in two stages: first, the over-all condition is determined and corrected; then, the
condition of fore-and-aft equilibrium is determined and the necessary adjustments
made. When the fore-and-aft trim is very
evident, the necessary corrections should be
combined with the correction for over-all
trim. When properly made, this analysis conveys a thorough understanding of the submarine's condition and indicates the corrective measures.
Certain terms have been established as
standard phraseology in describing the trim
of the submarine. These terms are factual
statements of conditions and also indicate
the procedure necessary to attain final trim.
a. Heavy over-all and heavy aft. The
entire phrase is necessary to describe conditions. Heavy over-all indicates negative buoyancy and heavy aft indicates that the fore-and-aft moments are not in equilibrium and
that there is too much weight aft. The remedy and order would be, "Pump from after
trim to sea."
h. Light over-all and light forward.
Light over-all indicates that the submarine
has positive buoyancy and light forward indicates the remedy: "Flood forward trim
c. All right over-all and heavy aft. This
indicates that the ship is in the condition of
neutral buoyancy and that equilibrium should
be established fore and aft by the adjustment
of ballast between the trim and auxiliary
tanks. This adjustment may be obtained by
any one of three methods:
1. Pump from after trim to forward
2. Pump from after trim to auxiliary.
3. Pump from auxiliary- to forward
d. All right over-all and all right fore
and aft. The submarine is in neutral buoyancy and is in equilibrium fore and aft; hence
it requires no trim adjustment.
It may be noted that the above trim
conditions might be expressed by different
phrasing. For instance, "heavy over-all and
heavy aft" might be described as "Heavy
over-all and light forward" and "Light over-all and light forward" might be phrased,
"Light over-all and heavy aft." However, the
standard phrasing is preferred. "Heavy
over-all and heavy aft" leaves no room for
doubt as to the condition or the remedy. As
the object of a standard phraseology is to
convey information concisely and efficiently,
it should be adhered to at all tines.
18B3. Initial trim. When the submarine
leaves the surface it is heavy over-all and
heavy forward, the negative tank having
been flooded to give negative buoyancy and
an initial down-angle. Nearing the specified
depth, the negative tank is blown and the
planesmen control the angle and depth of the
ship. The diving officer now observes the
angle of the submarine. If the submarine is
heavy or light to such a degree that the
planesmen cannot maintain the depth without the assistance of the inclined surfaces of
the ship, the inclinometer indicates the corrective action. Should it be necessary to
carry an up-angle in order to hold depth, the
ship is heavy and ballast is pumped from the
auxiliary tank to sea until the planesmen
can hold depth on an even keel. In the case
of a down-angle, the auxiliary tank is flooded
from the sea.
During this first check, which is made
immediately on reaching ordered depth, the
boat is moving at the speed of submergence.
As the effects of inclined surfaces are proportional to speed, this first correction may
not be enough. The diving officer now orders
two-thirds speed and the angle is checked
again and corrected as before if necessary.
The speed is then reduced to one-third and
the check and correction repeated. This trimming operation is repeated until depth can be
maintained at slow speed with a zero bubble.
18B4. Final trim . When the ship is on an
even keel and moving at slow speed, the
analysis of fore-and-aft trim can be made.
If an excessive angle on the diving planes is
necessary to hold a zero bubble, the diving
officer orders a readjustment of the ballast in
the trim tanks until the planesmen can hold
a zero bubble with a minimum use of the
planes. As final trim is made at slow speed,
any subsequent change in angle requiring excessive use of the planes indicates a further
adjustment of fore-and-aft trim; any difficulty in maintaining depth indicates a correction of over-all condition
18B5. Summary. Over-all trim is the process
of attaining neutral buoyancy; final trim is
the establishment of fore-and-aft equilibrium
with neutral buoyancy. The foregoing description divides the procedure into two distinct phases and these are detailed as a sequence of operations. The experienced diving
officer will, however, recognize both conditions simultaneously, and combine the operations as dictated by his judgment. Thus he
may, in a minimum time, return speed control to the commanding officer by his report,
"Final trim," meaning "All right over-all
and all right fore and aft."
18B6. Special conditions. When diving, if
the submarine, is so badly out of trim that
the stern planesman cannot control the angle,
the diving officer must first correct the fore-and-aft trim, thus enabling the stern planesman to control the bubble, before attempting
any trim analysis. In this extreme condition,
it must be remembered that, for a given
speed, the forces resulting from the angle of
the submarine are greater than those resulting from the angle of the planes. Changes of
depth with way on, and carrying an angle,
do not necessarily indicate the over-all condition.
Consideration must be given to the
forces resulting from the speed and angle of
the submarine. Therefore, if the stern planesman cannot control the angle, and the depth
is changing in a direction contrary to that
desired, the most effective measure that may
be employed is that of reducing speed. For
example, if the submarine will not go down
while carrying all up-angle that cannot be
removed by the stern planesman, it must slow
down or stop. If the depth does not increase,
then, and only then, may it be concluded that
the ship is "light over-all and light forward."
Forward trim must be flooded until the stern
planesman obtains control of the bubble.
When control is obtained, the analysis and
correction of trim may be continued.
If the submarine is going down while
carrying a down-angle that cannot be removed by the stern planesman, it must slow
down or stop. If the depth continues to increase, then it may be concluded that the ship
is "heavy over-all and heavy forward." Variable ballast must be pumped from forward
trim to sea until the stern planesman can
control the angle. It is possible that the condition of trim was "all right over-all and
heavy forward." The submarine was in a
condition of neutral buoyancy and retained
its initial downward motion after the force
resulting from speed and angle had been re-
moved. However, this fact did not become
known until after the downward motion had
18B7. Effect of backing while submerged .
When the submarine has an excessively large
down-angle during submergence, and it is
desired to stop its downward motion, it has
been stated that part of the force that is
driving it down may be removed by stopping
the propellers. However, due to the slow rate
of deceleration, the downward motion will
continue for a time after the propellers are
stopped. The quickest way of stopping downward motion is to "stop and back." The
reversed propellers tend to force the stern
down and the ship squats. This also tends
to remove the down-angle. Hence, the procedure for checking downward motion and
down-angle when the planes are ineffective
is "stop, back, and blow." These measures
are resorted to in that order, using one, two,
or all, depending upon the emergency.
18C1. General principles. Surfacing must
be done with caution. The submarine is first
brought to periscope depth and a thorough
search is made of the surrounding area.
When assured that surfacing is safe, the preliminary order, "Stand by to surface," warns
the personnel that the signal may be expected.
At the sounding of the signal, three
blasts of the diving alarm, or the passing
of the word "Surface, Surface, Surface," the
various actions necessary are performed.
The bow planes are placed on ten degrees
dive and rigged in automatically unless the
conning officer gives other instructions. A
report, "Bow planes rigged in," is made to the
conning officer. Speed is increased to about
6 knots to give maximum lift. Due to the
up-angle on the ship, the increased speed
makes the inclined surface of the hull effective and the resultant lift raises the ship.
The stern planes are used to limit the up-angle to about 5 degrees. The up-angle may
be increased by blowing the bow buoyancy
tank. Blowing the safety tank increases the
positive buoyancy. However, this is not usually done.
The main ballast tanks are partially
blown to surface normally. After surfacing,
the high-pressure air is secured and the blow
is completed with the low-pressure blowers.
During submergence, certain tanks are
vented inboard, and torpedoes may be fired.
This causes a consequent rise of pressure
within the ship. On occasion this may be a
rise of several inches. It has been found by
experience that release of the energy in the
large volume of air within the pressure hull
may result in injury to personnel, damage to
hatch gaskets, or the loss of loose gear caught
in the rush of escaping air through an open
Sealing the lower conning tower hatch
permits immediate opening of the upper
hatch since the relatively small volume of air
in the conning tower can be released without
danger. This procedure expedites the movement of personnel to the bridge.
When the decks are awash, the conning
tower hatch is opened and the commanding
officer goes to the bridge. In the meantime,
all stations are alert and prepared to dive
at once. The safety of the ship demands that
nothing interfere with an emergency dive,
should it become necessary. When the commanding officer is satisfied with surface conditions, the announcement, "All clear" will
indicate that the submarine is to remain on
the surface and the remainder of the surfacing routine is carried out.
During this interval, the low-pressure
blowers, using air from within the ship, are
completing the blowing of the main ballast
tanks and reducing the pressure within the
hull. Usually the pressure is equalized before
the lower conning tower hatch is opened. The
engine air induction and hull outboard ventilation valves are opened on orders from the
bridge. Propulsion is shifted to the main
engines. The safety tank is flooded, the low-pressure blowers are secured after 15 minutes running, or when the tanks are dry, and
normal surface routine is again assumed.
18D1. Diving and submerged.
a. "Rig ship for dive." The order to
carry out the preparations for diving listed
in Section 18A4.
b. "Ship rigged for dive," or "Ship rigged for dive except ------------- " A report indicating the accomplishment of the above order.
c. "Clear the bridge." A usual preliminary to the diving signal. All personnel, unless excepted, lay below on the double.
d. "Bleed air." An order to bleed air
into the submarine.
e. "Pressure in the boat." The report
indicating that the hull is sealed.
f. "Green board." The report meaning
that all hull openings are closed, as indicated
by the Christmas tree.
g. "Six, (five, etc.) feet." An order to
the diving officer, or the bow planesman,
giving the desired depth.
h. "Ease the bubble." "Zero bubble."
"Five degrees down bubble." Orders to the
stern planesman giving the angle desired on
i. "Shut bow buoyancy vent." "Shut
the main vents." "Open negative flood." Orders governing the operation of the various
flood valves and main vents.
j. "Vent safety." Open safety vent,
then, after tank has vented, shut the vent
k. "Blow safety." "Blow negative."
"Blow all main ballast." Orders to the air
manifold watch to blow the designated tank
l. "Secure the air." "Secure the air to
bow buoyancy." The order to stop blowing
all tanks, or the designated tank.
m. "Cycle the vents." Given when it is
desired to vent safety, bow buoyancy, and
the main ballast tanks in succession.
n. "Full rise on the bow planes." "Five
degrees dive on the stern planes," Orders to
the planesman, giving the angle desired on
the diving planes.
o. "Pump from forward trim to after
trim." "Flood auxiliary from sea." "Blow from forward trim to sea." "Pump from
auxiliary to after trim five hundred pounds."
"Secure the pumping." Orders to the trim
and air manifold watches, used in shifting
p. "Start the low-pressure blower, blow
all main ballast." "Secure the air to number
one." "Secure the low-pressure blower."
Orders governing the operation of the low-pressure blowers.
q. "Pressure equalized." The report
that the air pressure inside the submarine is
the same as that of the atmosphere.
r. "Take her down." Increase depth as
rapidly as possible. Exact depth will be
s. "Rig for surface." The order to
place the ship in the normal peacetime surface cruising condition.
t. "Open bulkhead flappers, and recirculate." Given after the dive has been made
and conditions are satisfactory.
u. "Low-pressure blower secured, all
main ballast tanks dry, safety and negative
flooded, conning tower hatch and main induction open, depth eighteen feet." A typical
report by the diving officer, giving the conditions upon completion of surfacing.