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OFFENSIVE AND PROTECTIVE OPS
Submarines are
most effective, and thus most dangerous when they are able to
remain undetected. As such, their stealth abilities which will
allow them the opportunity to approach a prospective target
and mount an offensive maneuver is their greatest asset. The
goal of Anti Submarine Warfare (ASW) is, simply stated, any
action and operation designed to deny the enemy the
opportunity to make effective use of their submarines.
Anti submarine
operations can be categorized into two actions: Offensive or
Protective. Offensive actions provides the ASW forces
the initiative and first strike capabilities in an effort to
disrupt and/or destroy enemy submarine ops. Attacks against
submarine bases, building yards, and combat units would be
examples. Convoy escorts, screens, and harbor defense describe
protective operations. Other well known tactics such as
mine laying and hunter/killer groups could actually be
described as either offensive or protective in nature.
In today's
modern Navy, all destroyer type vessels (DD, DDG, FF and FFG)
and cruisers (CG, CGN) are capable of anti submarine warfare.
Although cruisers are principally responsible for anti air
combat. During World War II, the responsibility for protecting
convoys and battlegroups against submarine attacks rested on
the destroyers
(DD),
destroyer escorts
(DE),
sub chasers (SC),
frigates, cutters (USCG) and corvettes. Those ships which
comprise ASW units may be formed as a screen to protect a main
body or the may be separately organized as hunter killer
groups to provide a trailing support for another surface
force.
SCREENS
Naval
terminology defines a screen
as
an organized, predetermined arrangement of warships, (often in
combination with aircraft) which is responsible for the
overall protection of the convoy or main body from attack by
enemy submarines or aircraft. Once the convoy departed port on
its way toward the final destination, the escorting ships
would take their assigned station and proceed with the group,
at times assuming the role of a shepherd rounding up the slow
moving stragglers and returning them to the relative safety on
group. Often, merchants who were unable to maintain the
general speed of the convoy were either ordered to return to
the port of departure to await a convoy which matched its
abilities or they would continue on alone and at the mercy of
the waiting U-Boats. Today's Navy utilizes several different
type of
screen formations: SECTOR,
SKELETON, HELICOPTER WINDLINE and DEPARTURE/ENTRY. A fifth
type of screen known as the "circular" screen is used only
during certain conditions, but this method of convoy
protection was employed extensively during World War II. It
allows for easy maintenance of both the ship's assigned
station and of communication between other vessels. Click on
the diagram above for a larger image depicting a typical
WW II .
Contact Classifications
"Sonar contact
bearing 325". During WW II, in addition to a visual sighting,
contacts would be made with enemy submarines by either Sonar)
or radar. The likelihood that any of the three methods had
been able to accurately identify or detect the presence of an
enemy submarine in the area requires that the contact be
initially categorized into one of four possible
classifications. As the investigation proceeds, the contact
classifications can be either upgraded or degraded as
necessary.
A.
Low Confidence: A contact that cannot be regarded
as a nonsubmarine and which requires further investigation
B.
High Confidence: A contact which, from evidence
available, is firmly believed to be a submarine but does
not meet the criteria for PROBSUB.
COMBAT INFORMATION CENTER
As technology
advanced and improvements were made to radar, sonar and radio
communication abilities, it became abundantly clear that one
man, the commanding officer, could not reasonably be expected
to sort through the myriad of available information and
develop an effective plan. The need arose for a way to
evaluate the often tremendous amounts of intelligence and
utilize the reported data in an effort to formulate a
coordinated attack. The result was the development of the
"nerve center" of a unit's ASW operations: the Combat
Information Center (CIC). Similar in scope to a military field
headquarters, the CIC collected, organized, evaluated and
processed the information provided maintaining an overall, up
to date picture of the battle scene. When authorized, the CIC
would also coordinate the actions of the various forces
involved (aircraft, weapons, other escort and merchant vessels
etc). When required, the activities of the CIC also assisted
the commander in search and rescue, navigation, piloting and
tactical maneuvers.
On board a WW II
destroyer, the charthouse had been the original location for
receiving information concerning enemy contacts. As ASW
activities grew in complexity, so did the need for improved
facilities for the ability to present a comprehensive view of
the tactical situation and by 1942 a separate room was
eventually designated for this function. Under the command of
the ship's Executive Officer, the CIC would maintain a plot of
the action as it unfolded as well as a situation (strategic)
map of the disposition of both friendly and enemy units over a
large area. In addition, the CIC developed a status board or
flow chart which was a time based record of contacts,
intelligence and ASW operations.
Most critical
was the geographic plot. Often during the course of an attack
on an enemy submarine sonar contact could be lost, especially
immediately following a depth charge run or following a high
speed maneuver by a surface ship (high speed course changes
would cause a "knuckle" which can return a solid sonar echo) .
The maintaining of an accurate plot was essential if the ASW
unit was to hope to regain contact. The tactic generally
employed in regaining a lost contact was to turn 60° to 90°
after the attack. If sonar contact is not made at this time a
search arc of not greater than 60° was ordered. Once contact
had been regained it was critical to prevent allowing the
enemy submarine from getting within the destroyers "baffles"
(roughly astern of the ship - quarter to quarter). Sonar
contact cannot be maintained in this area. Once in position,
the ASW unit then continues the attack.
SEARCH TYPES
When a contact
is gained or a report of a submarine is received, ships may be
detached from the screen or support group to form a search
attack unit (SAU). An SAU is one or more vessels which are
organized into a tactical force to hunt down and destroy
submarines. The group proceeds to the contact area and begins
searching for the submarine, based on the information
provided. Aircraft when available, historically proven to be a
tremendous benefit as evidenced during the Battle of the
Atlantic, can assist in detecting, localizing and attacking
the sub. An ASW search is a coordinated investigation of an
area to determine the presence of the suspected enemy. The
search can be conducted by ships, aircraft or a combination of
the two.
There are
four basic search types:
Intercept, area,
lost contact and close search. The type of
search conducted depends upon the purpose of the search and
the area being covered.
INTERCEPT
SEARCH - A form of close search used when a sub is in
position to threaten the main body. Because the area in
which the interception is made is a moving and expanding
one, units must arrive in the area as soon as possible.
AREA SEARCH
- Used when the location of the reported sub is not
definitely known. The size of the area and therefore the
number of units required depends on the time elapsed since
the probability area was established and on the accuracy of
the report. Aircraft are the most effective in this type of
search.
LOST
CONTACT SEARCH - Generally started immediately after
contact is lost. The search is normally of short duration,
usually being terminated after about 15 minutes.
CLOSE
SEARCH - A small area search used after a lost contact
search fails to locate the sub or when it is believed that a
lost contact search will not contain the sub.
The basic search
patterns employed are rectangular, sector, and
expanding square.
Sector
searches are usually long range in nature to provide the
earliest possible warning.
An expanding
square is a rectangular pattern starting at the last known
position of contact.
SWEEPS
A sweep is the
active investigation of an area. It can be broad in nature
when moving in conjunction with the track of the main body or
it can include a specific area after an enemy contact has been
made relative to the main body's position. The following are
general descriptions of a basic search/sweep plans:
SEARCH PLAN 1
-
A single sweep
through an area using a broad zigzag if necessary to widen
the front. This allows for coverage of the anticipated track
of the main body and is often useful for small areas or if
it is necessary to carry out a rapid but low probability (of
a success) search.
The expanding
square can be employed based on a submarine contacts last
reported position or at a search center - a reference point
other than a reported location. Escort vessels would travel
in a loose line abreast.
A series of
parallel sweeps through successive sections of an area that
provide broad coverage but at a slow rate of speed.
Random sweeps
in series. This method provides maximum deception.
Search Plan 1 is
an intercept search of a moving area, the size and position of
which depe nds on an
estimate of the submarine's probable course of action. If the
area is large and time permits a series of sweeps across the
area is employed. If the submarine is assumed to be closing
the main body, units are required to keep between the
submarine and the force. Time will thus usually permit only a
single sweep of the area.
SEARCH
PLAN 2
Search Plan
2 is basically a lost contact search used by two ships
against a slow speed contact. This pattern employs a left
and right plan oriented to an axis that passes through the
last known contact position. One ship is designated as the
"directing ship" and is responsible for for coordinating and
executing the search.
The
utilization of the "Left" or "Right" plan depends on the
location of the directing ship. If a right plan is used, the
directing ship is to the right of a predetermined axis and
all turns are made to the right. A left plan finds the
directing ship to the left of the axis and all turns would
then be to the left. The two ships heading in opposite
directions pass close by the last know point of contact and
conducts a general search pattern that would cover the
possible location of the sub.
ANTI SUBMARINE ATTACKS 
Once positive
information on the position of a submarine is known, it is now
time for action. There are two types of ASW attacks which will
be conducted by the escorting vessels: URGENT and DELIBERATE.
An urgent
attack, normally delivered with maximum speed but with
minimum accuracy, is the response generated when the initial
threat, or the continued threat, of attack by a submarine on
the protected body is detected and imminent. It is a defensive
tactic on the part of the escorting units designed to throw
the attacking submarine "off balance" by forcing it to
submerge if surfaced or to transfer the initiative by
harassing the sub into undertaking evasive maneuvers and
turning the "hunter into the hunted."
A
deliberate attack is designed to kill and is undertaken
immediately after an urgent attack. It is delivered with
maximum accuracy and the maximum firepower available. The goal
is to obviously destroy the submarine and completely eliminate
any continued threat.
BASIC ASW
TACTICS
In general
terms, anti submarine units were responsible for the
protection of harbors, coastal waters and traffic routes by
way of patrolling as well as serving as the guardians of
merchant convoys and battlegroups they escorted.
Regardless of
the duty, the transition from a defensive to an offensive
posture was often rapid for the ASW unit. The actual doctrine
established by the Navy was not particularly well defined
during the early stages of the war however. Much of what the
USN learned regarding ASW tactics was often literally hit or
miss and they relied heavily on the experience of the
Britain's Royal Navy for education.
Upon
receiving a report of a possible submarine, one or more ASW
units would break off from the convoy to investigate. This
often left some portion of the transiting group vulnerable
(especially during wolfpack attacks by U-Boats) which meant
that the vacated area now had to be covered by another anti
sub vessel. Once the contact had been confirmed, the primary
goal of the investigating ship was to disrupt the offensive
capabilities of the attacking submarine. The failure to
destroy the sub should not be considered as a negative result,
although ideally any damage or loss that could be inflicted
upon the enemy forces was a major bonus. Rather, the ability
to drive the sub down (known as the Hold Down) and
remove his offensive capabilities was truly the benchmark to
which success was measured. By forcing the submarine to
submerge below periscope depth in an attempt to avoid the
depth charges which were to follow, the submarine threat now
has been reduced . . . although not eliminated. If the depth
charging did not destroy the submarine, the effort to keep the
submarine deep would allow the convoy the opportunity to gain
precious amounts real estate, thereby putting greater distance
between them and the attacker. Hopefully, the submarine
remains below periscope depth long enough to be out of
effective range of the convoy and thus the attack has been
foiled. Prior to the utilization of Hunter/Killer groups,
convoys that were fortunate to have enough escorting vessels
to allow one or more to remain behind, tenaciously keeping
between the convoy and the submarine and forcing it to remain
submerged for extended hours, fared a much greater chance in
recording a kill then the convoys whose escort complement were
somewhat thin. In short, a successful escort effort was
measured in the amount of merchants who arrived to their
destination safely rather then by the number of enemy
submarines sunk. this is particularly true during the early
stages of the Battle of the Atlantic.
World War II
vintage submarines, while diesel driven when on the surface
were battery powered once submerged. The ASW units that were
able to remain on a contact and keep it under for extended
periods could eventually force the sub to expend its valuable
battery resources. Prior to Germany's use of the schnorkle
(which allowed a U-Boat to remain at periscope depth and use
their diesel engines for propulsion) the
maximum
submerged endurance of a sub was
approximately 50 hours. The purpose of the hold-down was to
keep the submarine submerged to a point of suffocation,
desperation or exhaustion. Once available oxygen and power was
down to a critical level, the submarine would have no choice
but to surface and duke it out with the destroyers waiting
above. Extended depth charging would also have a very powerful
effect on the nerves of the submarine crew. In a surface
battle, the favor would rest with the destroyers, although
many a wily U-Boat commander has escaped after many hours of
deep submergence and depth charging under the cover of
darkness. That is to say that the destroyermen had to be
particularly vigilant at nightfall. A submarine that could
surface undetected could engage its diesel engines and quite
possibly escape.
ASW ATTACK
The basic
destroyer attack procedure was to point the ship at the target
and head towards it at a moderate speed. Once the ship was
generally within 1,000 yards, sufficient sonar data regarding
the submarine's heading and speed should have been determined.
At that point, the destroyer's helm would maneuver on a
"collision course" with the target. Adjustments would be made
in the DD's course to account for the approximate depth of the
sub, calculating the amount of time it would take for a depth
charge to sink to the lethal level. Depth charges dropped from
the stern tracks would be in evenly spaced intervals. The port
and starboard throwers would send DC's approximately 50 yards
out on either side - forming an elongated diamond shaped
pattern. The goal was to pass just far enough ahead of the
submerged target and launch the DC's in the hopes that the
submarine's travel would take them right into the path of the
sinking ordnance. While it was not necessary for the ashcan
type depth charges to make contact with the sub to be
effective, they did need to detonate within close proximity.
Because much of the mechanics of this type of attack relied
largely
on guesswork, depth
charges were set for differing depths and the outcome of the
attack was often inconclusive. Destroyermen would search for
the telltale sign of the sinking or damaging of an enemy
submarine: An oil slick on the surface, floating decking,
Sonar reports of "breaking up" noises etc. A severely damaged
submarine might be forced to surface within range of the DD in
an effort to either outrun their attacker or duke it out with
their deck gun . . . or they might even scuttle their boat and
surrender.
THE CREEPING
ATTACK
There were
two important factors which a U-Boat captain could use to his
advantage while undergoing an attack from the surface escorts
above. The telltale screw signature of an escort was able to
be picked up by a U-Boat's hydrophones. While not as
sophisticated as today's sonar, the WWII soundman was able to
differentiate between a merchant vessel and a warship by the
noise generated by the ship's screws. Thus the commander of a
submarine could conduct evasive maneuvers based on the
intensity and location of the fast turning propellers. In
addition, while ASDIC (sonar) was a tremendous tool for the
convoy escorts in detecting enemy submarines, the echo ranging
impulses . . . the famous "pinging" which we are all familiar
with . . . which the transducer generated would reverberate
through the submarine's hull. As an approaching Destroyer drew
closer to the sub the echo impulses became shorter and it
could easily be rationalized that the ASW unit on the surface
was beginning an attack run and evasive action was necessary.
If however, the ASDIC pinging remain constant, it might be
assumed that the source was possibly in a search mode,
attempting to regain a contact and did not pose an immediate
threat nor signal an imminent attack run. Therefore, stealth
on the part of the U-Boat, generally by way of silent running
could be employed in an effort to escape. Both scenarios,
coupled with the temporary loss of contact which was often the
result of dropping depth charges, presented some major
challenges for the escort commanders. Captain Frederic John
Walker RN, renowned as one of the Allied heroes in the defeat
of the U-Boats during the Battle of the Atlantic, developed a
plan of attack which took these factors into account. The
"Creeping Attack", utilizing at least two escort vessels,
allowed for
a
"directing"
ship to maintain regular
active
sonar contact at a steady range and
bearing with the enemy sub while a second ship headed at a
speed of not more then five knots towards the last known
position of the submarine,
with its' sonar equipment off.
Once in position, escort number two would release his depth
charges on the command of the directing ship in the hopes that
his approach was not detected by the submarine.
As with all
ASW tactics, the creeping attack of course was not always 100%
successful. When this effort failed, Captain Walker would
often resort to another method which he developed called
"Operation Plaster". The name might be a bit of a give-away,
but it basically utilized three escort vessels in a moving
line abreast literally plastering an area with a large number
of depth charges set up to 550 feet at five second intervals.
A fourth or fifth ship would take station a distance away from
the activity while maintaining sonar contact with the target.
The steady stream of ordnance raining down on the enemy below
would virtually overwhelm the U-Boat and its destruction was
often certain.
TACTICAL ERRORS
Proficiency in
hunting submarines was not the US Navy's strong point during
early the early stages of the war . . . in fact, American
escorts accounted for a grand total of six enemy subs sunk
during the months of January through June of 1942. Germany was
turning out greater numbers of U-Boats every month and the
score sheet balance was tilting heavily in favor of the
Kriegsmarine. US destroyers had to even things up by doing
more then simply scaring the enemy away from convoys - they
had to sink submarines. Part of the problem can be
attributed to ineffective techniques and pure inexperience.
The challenge was that there was no established, workable ASW
doctrine. This was compounded by an equally important factor
which contributed heavily to the US Navy's overall
ineffectiveness: inadequate numbers of escorts assigned to
protect a convoy. There just weren't enough available at the
time to allow for one or two DD's to break away from the group
to hunt down an attacking U-Boat without leaving the convoy
vulnerable.
Samuel Eliot
Morison, in The History of the United States Naval
Operations in WW II (Volume I - The Battle of the Atlantic),
identifies six points which illustrates the most common
tactical errors
of an anti-submarine
attack:
-
A tendency to
drop depth charges too early in the attack, corresponding to
the common failure of anti-aircraft guns to give sufficient
"lead". Although mostly due to over eagerness, several cases
were explained by the failure to correct the relative speed
on the last minute turn by the target or the attacker, or an
acceleration by the attacker.
Sound
operators sometimes failed to "sweep" the target or to
inform the conning officer from which edge of it they were
reading the bearing.
There was a
tendency to economize on the expenditure of depth charges
and not throw a large enough pattern.
Attackers
(escorts) were often baffled by a standard submarine escape
tactic of getting inside the turning circle of the attacker
in such a manner as to force her sound operator to take
ranges on its wake rather than its hull or on "knuckles" in
the water caused by the sharp turn of the U-Boat's
propellers.
Although a
ship has only one chance out of fifteen to catch a submarine
after it has dived, the mathematically determined search
course which would give her that one chance in fifteen of
regaining a lost contact was not followed.
The old jinx
of communications continued to hamper anti-submarine warfare
even more then other branches of warfare because of the
imperative need for promptness. There was continued
improvements in ship-to-ship and ship-to-shore
communications; but as aircraft took an increasing share in
ASW, infinite trouble developed in plane-to-ship
communications.
SUMMARY
Once a
contact has been made and the pursuit initiated by the
destroyermen, the battle between the submarine and the surface
units becomes one of a cat and mouse game as well as a measure
of endurance. Maintaining contact was a key element of the
hunt for the anti submarine ship. Keeping the sub below
periscope depth and out of effective range of a passing convoy
was the
initial
goal. Forcing the
enemy to expose his location, whether submerged or on the
surface, to the point that the ASW unit could destroy it was
the payoff.
Resource
Notes:
Blair, Clay,
HITLER'S U-BOAT WAR: THE HUNTED, Random House, NY
1998
MacIntyre,
Capt. Donald., U-Boat Killer, NIP, Annapolis, 1975
Morison, Samuel Eliot, BATTLE OF THE ATLANTIC,
Little/Brown, 1947
NAVEDTRA 10776-A, SURFACE SHIP OPERATIONS, Naval
Education/Training Command, 1978
Pitt, Barrie, BATTLE OF THE ATLANTIC, Time Life, NY,
1977
Robertson, Terence, ESCORT COMMANDER, Nelson
Doubleday, NY. 1956
Roscoe, Theodore, US
DESTROYER OPERATIONS, US Naval Inst, Annapolis, 1953
Whinney,
Bob, THE U-BOAT PERIL, Blandford, UK, 1986
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