[formerly] CONFIDENTIAL [Declassified 17 Aug 72]
OFFICE OF NAVAL INTELLIGENCE
Washington, November 1, 1918.Upon
the recommendation of Operations-Aviation this study of the use of kite
balloons in escorts, made by the planning section, is published for the
information of the naval service. This pamphlet is confidential and for
the use of commissioned officers only.
ROGER WELLES
Rear Admiral, U. S. Navy,
Director of Naval Intelligence
KITE BALLOONS IN ESCORTS.
PLANNING SECTION-MEMORANDUM.
PROBLEM.
Kite balloons being available for use with escort vessels, the following questions arise:
1. Should kite balloons be used by vessels escorting convoys?
2. If escort vessels use kite balloons, what are the principles governing their use?
In
considering these questions all available publications and reports have
been carefully studied and freely used in the notes that follow.
The following information is pertinent:
(1)
In July, 1917, experiments were carried out with a kite balloon by a
destroyer. It was found that a kite balloon could trace the submarine
after her movement could no longer be seen from the bridge; but it is
doubtful if a kite balloon observer can follow a submarine that seeks
to escape by diving more than a minute longer than the same submarine
could be followed from the bridge. When the submarine is leaking oil
the kite balloon is more useful in the chase than at any other time.
(2)
In July, 1917, the Grand Fleet Destroyers made an experimental hunt for
submarines. The submarine was discovered on the surface 8 miles away.
Later, two periscopes were discovered, distance not stated.
(3)
Later two other submarines were discovered in the same hunt by the kite
balloons, distance not stated. No result of the contact, except that
the submarine remained submerged during daylight.
(4) On July 12, 1917, H. M. S.
Patriot
sighted a submarine on the surface at a distance of 28 miles. The
submarine submerged when kite balloon was distanced 6 miles. Submarine
came up when kite balloon was 4 miles away and immediately submerged.
Patriot was directed to the spot by the kite balloon and an attack was made; submarine was probably destroyed.
(5)
On May 27, 1918, a convoy was attacked while escorted by a kite
balloon. The attack was delivered five minutes after the balloon was
hauled down to change observers. This was the first instance on record
of an attack on the convoy while being escorted by a kite balloon. A
second convoy was attacked on September 3, 1918, when escorted by a
kite balloon; one vessel was sunk.
The British believe that
enemy submarines feel that they incur no great danger while being
sighted from kite balloons at a distance. British publications give the
visibility of kite balloons in clear weather at about 20 miles.
Visibility varies with light, background, color of balloon, relative
positions of balloon and observing vessel.
(6) It is known, of
course, that even when convoys are not accompanied by kite balloons,
submarines as a rule sight convoys before they themselves are sighted.
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(7) At twilight in clear weather a kite balloon becomes
increasingly visible from all bearings, and remains so until it is
quite dark. Under these conditions it is probable that a submarine can
come to the surface at some distance from the kite balloon and follow
it without fear of detection.
(8) Observations from kite balloons are much less efficient when wind is blowing.
(9) When there are white caps on the water the chances of seeing a periscope from a balloon are small.
(10)
Recent records covering British operations indicate that a kite balloon
has to cruise over 30,000 miles to sight a submarine. The conclusion
is, of course, that as a rule--
1. The submarine sees the kite balloon first.
2. The submarine submerges very soon after the kite balloon is sighted.
Considering now the questions to be decided, viz.:
1. Should kite balloons be used by vessels escorting convoys?
2. If escort vessels use kite balloons, what are the principles governing their use?
It
is evident that the answer to question (1) depends in part upon the
answer to question (2), so we shall investigate the principles
governing the use of kite balloons first.
The kite balloon has but one
direct use and that is
to get information; it has but one drawback that need be considered here, and that is that it
gives
information to the enemy. The real problem for the kite balloon
therefore is to get as much useful information as possible, and to give
as little useful information as possible to enemy vessels.
The
indirect use of a kite balloon is measured by its effect on enemy
submarines. They nearly always submerge in time to avoid being seen
from the balloon while they are still on the surface, and thereby
voluntarily limit their maneuvering power.
There are two ways of using kite balloons:
(1) In close escort positions. Here the kite balloon vessel zig-zags close to the convoy.
(2)
In extended patrol positions. Here the kite balloons are at visibility
distance from the convoy in thick weather and at about 12 miles from
the convoy in clear weather.
The functions of the kite balloon in close escort positions-where it usually zigzags across the front of the convoys are-
(1)
To sight any submarine which through a bad lookout or through taking
chances, stays on the surface with the kite balloon in sight.
(2) To sight submarines that attempt to attack in time to give warning and to direct a counter attack.
(3) To warn convoy of browning shots.
(4)
To limit the submarine[`]s maneuvering area on the surface so that if
the submarine be in the rear of the convoy it will have to make a very
wide detour to get ahead of the convoy in position for attack,
undiscovered.
(5) To prevent trailing of convoy by dropping astern of convoy just before dark.
(6) To keep submarines submerged after an attack.
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The close escort position is the one that gives the maximum
information to the enemy submarine. It makes a conspicuous marker of
the convoy's position and thereby enables the submarine to communicate
the convoy's position and movements to submarines better placed for
attack. It is also quite possible for the sighting submarine itself to
gain a position for attack by a wide detour.
The principal advantages of the close escort position are:
(1) Readiness for counter attack.
Comment.--Unless
the submarine is leaking oil the kite balloon will probably not guide
the attacking vessel more efficiently than it could be guided from the
bridge for more than one additional minute--once the attack is
delivered.
(2) Protection against browning shots through warnings.
Comment.-Taking into consideration: (
a) That the kite balloon has not over two observers.
(
b) That the browning shot torpedo will not be in flight more than three minutes, and more often two minutes.
(
c) That an appreciable interval is required to give the warning.
(
d) That the warning can not tell each vessel the relative bearing of the torpedo.
We
conclude that the extra protection given by kite balloons against
browning shots is about one minute's earlier notice of danger to the
convoy.
(3) Bluffing the submarine.
Comment.--Recent evidence indicates that this element may soon be negligible.
From the above in conjunction with the operating experiences of kite balloons in the presence of submarines we conclude:
That
it is not profitable to use kite balloons in close escort positions
except in waters where convoy routes are well known-and during weather
when visibility is very limited.The extended patrol for
escort of convoys is discussed in various publications. Attention is
invited particularly to O. N. I. No. 29 of February, 1918.
The functions of the kite balloon in extended patrol positions are similar to those in close escort positions.
Every
convoy carries with it an area within which a submarine may maneuver
submerged into position for attack on the convoy. The width of the area
is twice the visibility of the convoy from the submarine's
periscope--about 14 miles in clear weather plus the length of the
convoy front. The area extends an indefinite distance ahead of the
convoy.
The afterside of the area is bounded by an irregular
line dependent on the formation and speed of the convoy, the speed and
radius of the submarine when submerged, and the range of the submarine
torpedoes.
This area is called the "diving danger area."
A
similar area known as the "surface danger area" includes and extends
beyond the "diving danger area" on the flanks and rear by an amount
equal to the difference in visibility of the convoy from a submarine
submerged and from a submarine on the surface. In clear
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weather the "surface danger area" may be taken to be 22 miles in width.
The
flank boundaries of both the "diving danger area" and the "surface
danger area" are determined by visibility from the submarine, because
the presumption is that the submarine can not maneuver for attack when
it can not see. The development of listening apparatus may in the near
future extend the "diving danger area" by the flanks--to twice the
listening radius rather than to twice the visibility--provided the
submerged radius of the submarine keeps pace with the listening radius.
Extended patrol vessels are vessels stationed at visibility distance from a convoy with the object
(
a) Of limiting the submarine's freedom of action on the surface and of preventing the submarines from sighting the convoy.
(
b) Of sighting any submarine that does not dive immediately upon sighting the patrol vessel.
If the patrol vessel carries a kite balloon the principles of extended patrol are not thereby altered.
If
the patrol vessels are stationed inside the "diving danger area" they
may sight a submarine but the submarine may still be able to maneuver
submerged so as to attack. If, however, the extended patrol vessels are
stationed outside the "diving danger area" and in such position as to
sight any submarine in or near that part of the "surface danger area"
not common to the "diving danger area," any submarine there sighted
will have to dive, and by diving will lose all chance of successful
attack on the convoy, since it will have dived without sighting the
convoy and without knowledge of its whereabouts.
When the convoy
is escorted by antisubmarine vessels it is reasonably safe to
assume--for all except the slowest convoys--that no submarine will be
able to maneuver submerged successfully for attack if it first sights
the convoy when the convoy already has the submarine abaft the beam.
In
stationing extended escort vessels care should be taken that the range
of vision astern is such that no submarine can reach the "diving danger
area" on the surface without being observed either by the extended
patrol or the close escort.
The following table gives the bearing in points from right ahead on which the extended escorts should be from the convoy guide:
TThe submarine can make these same deductions if it sights a single
vessel of war; so that practically the only information which the kite
balloon gives to the submarine is earlier information of the presence
of a vessel in a given direction, and correspondingly early information
of the general course of that vessel. This earlier information is
measured by the relation of the two circles of visibility (1) of the
vessel, (2) of the kite balloon. The atmospheric conditions modify very
greatly the relation of these circles of visibility. In clear weather
the kite balloon would probably be sighted twice as far as the vessel.
In thick weather the vessel itself might be sighted first.
(2) That
the submarine sighting the balloon will very likely be attracted by it
even to the extent of voluntarily leaving the "diving danger area."
(3) That all submarines outside the "diving danger area" will be prevented from entering that area except by chance.
(4) That the trailing of convoys will be prevented.
(5) Any submarine sighted can be kept submerged until convoy has passed or until dark.
The
practicability of using kite balloons in bad weather or on long voyages
has not been considered. We assume that decision in each instance as to
whether or not to take balloons in tow will be based upon operating
experience to date and a forecast of conditions likely to be
encountered.
As to question (1), it is not profitable to use kite balloons in close escort positions except--
(1) In waters where convoy routes are well known.
(2) During weather when visibility is very limited.
It is profitable to use kite balloons in extended escort positions in accordance with the principles already explained, viz--
(1) On the bearings given in the table at the bottom of page 8.
(2) At visibility distance from the convoy, except that in clear weather this distance shall not exceed 12 miles.
.--One on each bow, in extended escort positions given above, to make wide zigzag southward from extended escort positions.
.--On one bow in extended escort position crossing occasionally to the other bow and never lingering ahead of the convoy.
(3) [sic] With moderate and with low visibility--that is, when kite balloon will not be seen farther than convoy is seen--
--One in each of the close escort positions, zigzagging so as to cover the front of the convoy and the wing columns.
.--At close escort distance, ahead of convoy and covering the whole front with zigzags.
(4) When there is but one kite balloon with a convoy, it should as a rule be stationed:
(1) To windward of the convoy.
(2) On the sunny side of the convoy.
(3) On the side nearest the moon.
(4)
On the opposite side to the rising sun at dawn moving around to other
side at sunrise. (1), (2), and (3), to be at such distance from the
convoy that the submarine must dive before sighting the convoy and be
unable to come to the surface between the balloon and the convoy
without being seen.
(5) At twilight kite balloons should drop
back by the flanks as the light fails to positions on the quarters of
the convoy, keeping as far away as possible from the convoy without
losing sight of it and not closing up until quite dark. If during this
time convoy alters course after dark, kite balloons should stand off on
a different course and not rejoin until quite dark, then take close
escort positions.
(6) If in sight of land, or if the area ahead
of the convoy is being patrolled to the limit of visibility of the kite
balloon, kite balloon should be stationed in the close escort position
in all visibilities.
(7) Extended patrol should not be used until the minimum requirements of close escort have been met.
Approved
as a preliminary study of the subject of the use of kite balloons in
escorts, paper to be mimeographed, and to be given wide distribution to
forces for information and inviting comment, in order that a definite
doctrine and plan covering the subject may be developed.
Source: "ONI Publications, WWI" ZV file, Navy Department Library.
