LCACs IN SUPPORT OF THE AMPHIBIOUS LANDING
AUTHOR LTCMDR. Ronald L. Aasland, USN
CSC 1991
SUBJECT AREA - Operations
LCACs IN SUPPORT OF THE AMPHIBIOUS LANDING
Over the past two centuries of the U.S. Marine Corps'
existence, the military had witnessed a transformation of the
Corps from a law enforcement and Naval base security role to an
organization tacked with the vital role of projecting U.S.
military power ashore through amphibious operations. This
evolution occurred slowly until by 1929, "it was well
established that the role of the Marine Corps was to provide a
small well-trained amphibious assault force to seize and occupy
bases for fleet operations." (8:28)
Throughout World War II, the Marine Corps continued to
refine its amphibious assault capabilities throughout the
Pacific Island hopping campaign. All aspects of the amphibious
assault were highly developed including the latest in assault
and landing crafts. These crafts were capable of transporting
troops and equipment ashore in sufficient numbers to constitute
the strength required for offensive land operations. Although
these crafts only moved at approximately eight knots, cruiser
and battleship fire support, along with close air support, kept
the enemy pinned down until the marines were established
ashore.
Since World War II, the advent of the helicopter added the
dimension of vertical envelopment and sped up the pace for the
buildup of power ashore. Unfortunately, assault and landing
crafts continued to plod ashore at between eight and ten knots.
Innovative development of surface crafts to keep pace with the
helicopter did not happen until the Navy purchased its first
six Landing Craft Air Cushion (LCAC) vehicles in 1986.
With the LCAC racing ashore at 40+ knots, the Navy and
Marine Corps both began reconsidering the concept of the Over-
the-Horizon (OTH) assault. Now ainphibious assaults could be
conducted in excess of 25 nautical miles from the beach and
achieve tactical surprise and/or keep the amphibious task force
out of the range of enemy coastal defensive weapons. (14:2)
From the surface side of the amphibious assault picture, it
looked as though the problem had been solved with regards to
rapidly building up the landing force from over the horizon.
Little did the Department of the Navy realize what budget cuts
of the 1990's would do to this impressive surface assault
platform.
As the Marine Corps moves forward in implementing the
Over-the Horizon amphibious assault, it will depend very
heavily on the capatibility of the LCAC. With Department of
Defense cutbacks in the procurement of amphibious ships and
LCACs, the ability of a Marine Expeditionary Brigade (MEB)
sized force to rapidly build its combat power ashore prior to
an enemy counterattack is seriously in doubt.
OUTLINE
LCACs IN SUPPORT OF THE AMPHIBIOUS LANDING
Thesis: As the Marine Corps moves forward in implementing the
Over-the-Horizon (OTH) amphibious assault, it will
depend very heavily on the capability of the LCAC.
With Department of Defense cutbacks in procurement of
amphibious ships and LCACs, the ability of the Marine
Corps to rapidly buildup its combat power ashore prior
to an enemy counterattack is seriously in doubt.
Outline:
I. Historical perspective.
A. Development of early amphibious vechicles
B. Development of early amphibious doctrine
C. Pacific lessons learned
D. Present application
II. LCAC capabilities and limitations.
A. Characteristics
B. Capabilities
C. Survivability
D. Limitations
III. The Over-the-Horizon Assault.
A. LCAC cycle time
B. MEB/LCAC composition
C. Total lift requirements
IV. Analysis.
A. Lack of LCACs/LCAC capable ships
B. MEB raid versus forcible entry
EXECUTIVE SUMMARY
LCACs IN SUPPORT OF THE AMPHIBIOUS LANDING
Thesis: As the Marine Corps moves forward in implementing the
Over-the-Horizon (OTH) amphibious assault, it will
depend very heavily on the capability of the LCAC.
With Department of Defense cutbacks in procurement of
amphibious ships and LCACs, the ability of the Marine
Corps to rapidly buildup its combat power ashore prior
to an enemy counterattack is seriously in doubt.
Issue: This paper presents an overview of the Landing Craft
Air Cushion (LCAC) and its ability to support the amphibious
surface assault. An historical review of amphibious vehicles
and doctrine lays the foundation for the requirements of such a
landing craft. An analysis of the LCAC's characteristics,
capabilities, survivability, and limitations point out the
utility and necessity of the LCAC in modern amphibious
warfare. Due to Department of Defense cutbacks in procurement
spending, the Navy has cut its total number of LCAC capable
ships and overall LCAC program. This reduction in a program so
increasingly vital to the amphibious surface assault force,
seriously brings into question whether U.S. Naval forces will
be capable of conducting forcible entry.
Conclusion: Only the continued procurement of the LHD and LSD
class ships along with the full complement of 104 originally
planned LCACs will ensure the forcible entry capability of U.S.
Naval amphibious forces.
HISTORICAL PERSPECTIVE
During the early stages of the development of amphibious
doctrine, it was quickly recognized that the ship-to-shore
movement was a particularly vulnerable time for the troops.
Jeter Isely in his book on the historical and doctrinal
developments of amphibious warfare writes,
Therefore the main problem in planning a ship-to-
shore movement is to get troops disembarked into
their boats rapidly and in the right order, and to
dispatch the landing craft to the beach as quickly
as possible in formations that will reduce the
danger of being hit. (8:42)
Landing crafts were developed by several contractors, all of
which exhibited some innovative concepts, but limited by
technology could still do no more than eight knots.
Most of the changes and advances in the amphibious warfare
concept came from lessons learned during the World War II
Pacific Island hopping campaign. With many of the islands and
atolls surrounded by coral reefs, a craft was required which
could both swim and climb over reefs, if required, in order to
deliver its troops to the beach. The amphibian tractor, which
had originally been intended chiefly for logistical employment,
was adapted to become one of the most important tactical
weapons of the war.
Tarawa illustrated both the utility of these
vehicles and the folly of not having them on hand
in large numbers. Never again in the Pacific War
were assault troops to be handicapped by serious
shortages of this vital piece of equipment. Later
the same machine was armored and armed with guns
or howitzers and employed to lead the first waves
of troops into the shore. (8:583)
However, the most significant and decisive progress of
amphibious warfare was in the field of naval gunfire support.
This progress was achieved through the assimilation of lessons
learned through the experience of assaulting well fortified and
defended Japanese-held islands.
At Okinawa... seven full days were allotted to
naval bombardment before the day the first troops
were put ashore on the main island of Ryukyus...
Clearly by the end of the war it was recognized
that in the absence of compelling reasons to the
contrary, an extensive period of prelanding naval
bombardment was one of the vital keys to amphibious
success. Adoption of such measures meant the
sacrifice of tactical and to a certain extent even
strategical surprise. (8:588)
Although telegraphing a proposed landing site to the
defenders of an isolated island through extensive shore
bombardment might be the prudent thing to do, it is
questionable when confronting a well-defended continental land
mass.
Where the enemy has powerful forces distributed
over an extensive area and a system of land
communications capable of massing these forces
rapidly in any desired spot, advanced warning of
the location of the key beaches which the attackers
intend to strike might well prove disastrous to
assault. It is not difficult to imagine, for
example, what would have happened to the attack
forces at the Normandy beaches in June 1944 if a
large naval task force had moved in several days
before the initial landing was to be made, if it
had commenced to shell the selected beaches and if
the Germans had correctly estimated the situation.
(8:598)
From these lessons we can learn that a rapid transit for
the troops during the ship-to-shore movement is essential to
minimize their exposure to enemy fires. This transit must also
be made in a landing craft capable of traversing obstacles on
the way to the beach. Since extensive prebombardment of the
shore may signal our intended landing site, the landing craft
must be capable of surviving the initial assault on prepared
and undefended beaches. As the OTH assault moves the
amphibious task force further away from the beach, naval
gunfire support ships can no longer provide essential shore
prebombardment making it essential that assault craft be
constructed to survive the initial assault.
LCAC CAPABILITIES AND LIMITATIONS
The advent of the LCAC in the amphibious force has added a
new dimension to the surface assault. Besides operating at
greater than four times the speed of conventional displacement
hull craft it is also capable of crossing approximately 73
percent of the world's coastlines as compared to 17 percent for
conventional crafts, greatly complicating a defender's task.
Weighing 87 1/2 tons, it carries a standard 60-ton payload,
or an overload 75-ton payload, on a cargo deck. Its gas
turbine propulsion and air cushion technology allow it to
travel at speeds in excess of 40 knots. This tremendous
versatility allows it to move troops and all equipment in the
current Marine Corps inventory.
The LCAC employs hovercraf t technology to skim
across the ocean surface on a cushion of air. It
has a range of 200 nautical miles. With a full
payload, it can travel at speeds in excess of 50
knots in sea state 2 and 40 knots in sea state 3.
Overloaded, it will still achieve 50 knots in Sea
state 2. Unconstrained by winds, tides, reefs,
underwater obstacles, mines, beach gradient and
beach traf f icability, the LCAC can cross the shore-
line and proceed inland at speeds up to 35 knots.
Ashore, it will cross 20-foot ditches and 5-foot
vertical obstacles, knock down small trees, and
climb gradients up to 13 percent. (1:75)
Launched from 10-100 miles offshore, the amphibious task
force can remain over the horizon, beyond the reach of shore-
based target acquisition systems. With the deployment of LHA,
LHD, and LSD-41 class amphibious ships, the aggregate numbers
of LCACs in an amphibious task force continues to increase.
For more technical data on the LCAC, see appendix A.
Click here to view image
This growing utilization and dependence of the Navy on the
LCAC has forced both the Navy and the Marine Corps to reflect
on the operational capabilities of these crafts. Faster than
conventional landing craft, they now require their own landing
beach during assault operations. Due to their range and speed,
they can easily outrange the task force to conduct advance
force operations or subsidiary operations. If an intended
landing site is heavily defended, the LCAC can shift to an
alternate site 10-15 miles away, allowing for buildup of the
force in a relatively benign area. (4:43)
As a large, heavy, air-cushion vehicle, the LCAC can
launch in sea states prohibitive for LCM/LCU operations. The
air-cushion buffering effect also provides a better ride than
displacement hull craft in all weather. This is an essential
concept when trying to land combat effective troops who have
been in transit for 30 to 60 minutes. An LCAC's RADAR and
navigation systems also allow for operations during adverse
weather.
Since the LCAC was designed for use in the OTH surface
assault, it was realized that this craft would have to be
capable of surviving the initial assault on defended beaches.
The most vulnerable area of an LCAC is its drive train and
exposed propulsion systems. (3:18) If it is known that a
landing must be conducted against a heavily defended beach, an
additional five tons of armor can be placed around the drive
train system to enhance survivability. However, the addition
of this armor has an impact on the handling and maneuverability
of the LCAC as well as reducing the overall payload.
Both bottom laid and deep water mines have always been a
principle concern of landing craft. With the LCAC, the hull is
protected by an air cushion which makes it virtually
invulnerable to deep water mines. (4:43) As the LCAC moves
into shallow water, its air cushion causes no pressure wave
characteristic of displacement hull crafts. It is thus less
vulnerable to shallow water bottom mines. Unless it suffers a
detonation directly under the LCAC, "offboard detonations of
shallow water mines and near-miss direct and indirect fires are
not considered to be significant problems." (4:43)
The "LCAC Survivability Study" conducted by the Center for
Naval Analysis determined that approximately 40 percent of the
air cushion's skirt could be destroyed and still maintain
enough cushion for operation. (3:6) Another vulnerability
study conducted independently by the Ballastic Research
Labratory concluded,
. . . that the LCAC was relatively invulnerable to
small-arms fire and artillery fragments. The
study also stated that only direct hits by large
explosive warheads greater than 30 mm would pose
a threat to the LCAC components. (12:77)
Yet, despite the tremendous capability of the LCAC, there
are some limitations and drawbacks to it use. Due to its size
and the design limitations of the LHA, only one LCAC vice four
LCUs can be transported by the LHA. This is a reduction in
payload capability from 660 short tons to approximately 60
short tons, a tremendous loss in surface lift capability.
The high profile of the LCAC also makes it a vulnerable
target as it approaches the beach. The two very noticeable
huge push propellers to the rear of the craft would be likely
targets for shore defenders. Once damaged, the propulsion
blades quickly disintegrate rendering the craft immobile.
Four lift fans provide the air cushion the LCAC rides on.
In the event these fans, the four Avco-Lycoming gas turbines,
or any part of a series of eight separate gearboxes are
damaged, a portion or all of the air cushion may be lost.
(13:1-2 to 1-3) Without the air cushion and having no wheels,
the LCAC is incapable of being towed. So even minor damage to
a vital engineering component could quickly strand an LCAC on a
hostile beach.
The LCAC has provided some tremendous advantages to the
surface lift and assault capability of the amphibious task
force. Yet this design which provides enhanced survivability
also inf licts additional vulnerabilities and limitations on the
LCAC.
THE OVER-THE-HORIZON ASSAULT
The Department of the Navy's "Amphibious Lift/Aviation
Requirements Study" of 1989, examined in detail the ability of
the LCAC to support a MEB-sized force when landing against
elements of a "classic" Soviet motorized rifle regiment (MRR).
It was estimated that in a high threat environment the lead
battalion of the MRR could engage within 90 minutes and that
subsequent battalions would arrive at intervals of 90 minutes.
This would result in full regimental strength between H+l80 to
H+270. A mid threat environment would result in a closure rate
of 90-110 minutes resulting in the MRR at full strength by
H+27O to H+330. In a low threat environment, the MRR could
achieve full strength in a least time of 330 minutes. (19:39)
Furthermore, it was determined that 84 LCAC lifts were
required to transport the surface assault components of the
MEB. (19:38) Two thirds of the force participated in the
surface assault while the remaining one third constituted the
vertical assault force. The capability of all assets were
utilized as fully as possible and cargo required in the initial
assault was included with the vehicles in the standard loads.
Assuming that the operation is to take place "over-the-
horizon" to enhance survivability of the amphibious task force
and minimize the possibility of detection, the initial assault
was launched at 25 nautical miles from the beach. Subsequent
operations were conducted from 20 nautical miles from the
beach. Not until the beachhead was secure would the amphibious
task force move to within sight of the beach.
Allowing for an LCAC operational speed of 40 knots to and
from-the beach, we can figure 68 minutes for transit. Five
minutes are required for entering/exiting the well deck and two
minutes for going on/off cushion and opening/closing the bow
and stern ramps. (19:A-4.5) This gives us a cycle time of 75
minutes for the initial assault wave. Subsequent waves would
operate from 20 nautical miles and require an additional l0
minutes to load and gripe vehicles to the LCAC. This would
result in about a 78 minute cycle time for the second and
subsequent assault waves.
Now is we look at the Navy ships in a standard MEB-sized
force we see that it normally consists of between 15 to 18
ships. A force consisting of 1 LCC, 1 LHD, 2 LHAs, 3 LPDs, 4
LSDs, and 4 LSTs would carry approximately 21 LCACs. The
"Amphibious Lift/Aviation Requirements Study" point out that 18
LCACs are required to support the surface ship-to-shore
movement in a low threat environment, 24 LCACs in a mid threat
and 30 LCACs in a high threat environment. To lift even 24
LCACs would require 25 of the 30 amphibious ships assigned to
the Second Fleet. (19:40)
ANALYSIS
A recent article in Navy Times points to the developing
problem in supporting a MEB -sized force. Proposed budget cuts
in the Department of Defense will terminate procurement of the
LHDs one short of the anticipated five for its class, four
short for the Whidbey Island class LSDs and hold LCACs to 64
vice 104. (17:8) This reduction in the procurement of LCACs
and LCAC capable ships along with the scheduled decommissioning
of the LPHs, LPDs, older class LSDs, and the LSTs will
seriously degrade the Navy's ability to project amphibious
power throughout the world.
Through procurement reductions in amphibious ships and
projected decommissions, we will be facing an amphibious
force of 30 ships on the East coast. With 25 required to
support a MEB-sized force there will only be five lift in
Second Fleet for yard repairs, contingency/special operations
and scheduled exercises/commitments This force of 25 ships
will also strip away all of the LHD/LHAs and two thirds of the
Whidbey Island class LSDs.
Assuming that the 64 LCACs will be roughly split between
the two coasts, we are only looking at a total of 32 LCACs on
each coast upon completion of procurement at the end of FY 98.
With some LCACs in maintenance cycles, damaged or being used
on special operations, it will be difficult to pull together 24
LCACs to support a MEB. The "Ship-to-Shore Movement" analysis
conducted by BDM Corporation concluded that LCACs would suffer
a 30 percent attrition during an amphibious assault. (2:14)
This subsequent loss of LCACs would have a tremendous impact in
the ability of the surface force to carry out and continue its
operations.
Going back to our earlier analysis of LCAC cycle time, we
can determine that provided 21 LCACs in our amphibious force,
75 to 78 minutes for cycle time and a requirement of 84 lifts,
it will take 309 minutes to land our surface assault force.
Our limitations allow us to reasonably counter a low threat
situation, but not a medium or high threat Situation. This
lack of required LCACs and LCAC capable ships gives us the
ability to project our amphibious power against an
unsophisticated, ill-defended opponent.
The limitation of our LCAC supported surface force will be
the execution of small raids or advanced force operations. In
the face of a mid to high level threat, the surface force lacks
the LCAC punch necessary to conduct a forcible entry. As the
Marine Corps continues to move forward in its implementation of
the over-the-horizon amphibious assault, it will depend ever
increasingly on the capability of the LCAC. Unfortunately,
with the Department of Defense's cutback in the procurement of
LCAC capable amphibious ships and LCACs themselves, the ability
of the Marine Corps to rapidly buildup its combat power ashore
prior to an enemy counterattack remains seriously in doubt. If
we are to maintain a credible amphibious assault force capable
of forcible entry, we must continue with our original
procurement plans to procure five LHAs, all of the LSDs and all
104 planned LCACs.
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