Iwo Jima Class LPH and Vertical Assault

The Iwo Jima class carrier was the first purpose built vertical assault (helicopter) amphibious ship.  In this post, we’re going to take a look at its original design rationale, abilities, and limitations and examine whether those have remained relevant today.
 
Here are some basic specifications for the seven ship class, built in the 1960’s: 

Iwo Jima Class LPH

The amphibious assault helicopter carrier (Landing Platform, Helicopter - LPH) traces its origin back to a 1946 Marine Corps study on the effects of atomic weapons on amphibious assaults.[1]  Marine leadership, 

… concluded that a few atomic bombs could easily destroy the concentrated shipping and also the beachhead of any classical amphibious assault.[1]

As described by Friedman[1], the Marines settled on the helicopter as the means to achieve physical dispersion of both ships at sea and troops on land.  The greater range of the helicopter would allow the host ships to more widely disperse and would allow the troops to land at more widely dispersed locations thus avoiding the concentrations that an atomic bomb would easily destroy.
 
Their decision was strongly influenced by the belief that helicopters would quickly and markedly advance in capabilities (range, speed, lift capacity) – a belief that turned out, disappointingly, to be only partially met.  Friedman goes on to describe some of the helicopter development issues which is, itself, a fascinating topic but outside the scope of this post.  I encourage you to read it yourself, if you’re so inclined.  It’s well worth the time.
 
The Marines, while eagerly adopting the helicopter as the assault transport vehicle also recognized the vulnerability of the helicopter on the battlefield.  Regarding helicopter transport capacity, 

Even larger helicopters were proposed, but the Marines were reluctant to adopt one that could lift many more than twenty men in view of the high vulnerability of individual craft.[1][emphasis added]

The Marines recognized that concentrating greater numbers of troops in a vehicle that was inherently non-survivable would be a mistake.  In comparison, today’s MV-22 transport is rated for 24-32 troops which raises the concentration of risk issue that the Marines were afraid of.  To be fair, most sources state that the MV-22 troop capacity is not actually achievable in real world applications.
 
What did helicopter assault mean for overall requirements?  The Marines were focused on division-strength assaults, 

The Marines concentrated on the requirements of a divisional assault, which were considerable. For example, a January 1951 study envisaged lifting 10,000 men and 3,000 to 4,000 short tons of material.  Total lift, then, would be 520 HRSs [ed. Sikorsky H-19] or 208 HR2Ss, which in turn would require, in the former case, 20 escort carriers with 20 helicopters each, accommodating 150 to 200 tons of cargo, 500 to 600 assault marines, and a 200-man helicopter squadron.[1]

This focus on division level assaults was a far cry from our current MEU/ARG (3-ship Amphibious Ready Group) and disaggregated ARG which employs the three ships of the ARG separately.  Of course, in the event of a genuine assault operation, multiple MEU/ARGs would aggregate to form MEBs (Marine Expeditionary Brigade) and MEFs (Marine Expeditionary Force) although these aggregations are never exercised and constitute a theoretical capability, only.  Further, with the elimination of tanks, reduction in artillery, elimination of heavy mortars, and lack of anti-air vehicles it is highly debatable that MEBs/MEFs are even combat effective anymore.
 
The Marines also considered the tactical usage of the helicopter, 

Tactically, the Marines considered a flight of ten helicopters best for effective control, so that helicopter carriers were generally designed to accommodate multiples of that unit.[1]

We see then, that the Marines of the time were focused on getting large numbers of helos/troops on the ground quickly as opposed to our current concept of slow, drawn out, one-at-a-time MV-22 landings due to the 250 ft aircraft-to-aircraft separations and immense cleared areas required for landing.
 
To their immense credit, the Marines didn’t just come up with wild ideas and implement them without any proof of concept - as we do today - they conducted actual exercises.  For example, 

… May 1948, 8 helicopters from the Palau simulated a full helicopter attack of 184 aircraft flying from six CVEs, to lift a complete regimental combat team which would seize a strategic crossroads inland of the beach.  … each HRP [Piasecki HRP tandem rotor helicopter] carried six passengers about ten miles from the carrier under heavy fighter cover.[1]

Note the use of fighter cover.  The exercises were tactically realistic as opposed to the unrealistic, set piece theater performances we call exercises today.
 
Following tests, the WWII escort carrier USS Thetis Bay was converted for helicopter operations to further test out the concept.
 
At that point, the Marines seemed fully committed to helicopter assault.  A Sep-1954 report stated, 

… over the next ten to fifteen years most existing attack cargo and transport (AKA and APA) ships would be replaced by helicopter carriers.  “This will be occasioned by the VTOL aircraft becoming the principal means of placing personnel ashore under assault conditions.  Supporting personnel and heavy equipment will still be landed by water-borne means but the majority of assault troops will be air-landed.”[1]

Ultimately, a new design LPH, the Iwo Jima class, was built along with several Essex class conversions.  The purpose-designed Iwo Jima class, not surprisingly, offered several significant advantages over the Essex conversions.  Even so, the design was not without its flaws, 

The amphibious force commanders criticized the Iwo Jima design for its “complete lack of landing craft, so that it is of doubtful utility under non-flying conditions and must depend on other types with landing craft to give it an over-the-beach capacity.[1]

This flaw eventually led to the development of the LHA design which incorporated both aviation and  a well deck to support waterborne landing craft.  Interestingly, we have returned to exactly the original flawed design with the new America class variants which have no well decks.
 
 
Discussion
 
Let’s examine several aspects of the original vertical assault concept that birthed the LPH.
 
Rationale
 
As noted, the original rationale was dispersal of ships and troops in response to the threat of atomic bombs.  The original Marine thinking was dominated by the fear of atomic warfare.  With the advent of Mutually Assured Destruction (MAD), that is no longer a concern.  Any use of atomic weapons would immediately escalate the war to a global nuclear war and eliminate the need for a localized amphibious assault.  In other words, no one is going to bother with an amphibious assault while waging a global nuclear war.  Thus, the original rationale is no longer valid and yet we have not modified our current thinking to account for it.
 
Strengths
 

• Helos allow the rapid transport of troops from a greater distance than waterborne landing craft.
• Troops can be delivered to safer or more strategically beneficial locations rather than to a central troop/beach concentration although safer locations also imply less operationally relevant and useful.
• The greater range of the helos allows greater separation of the helicopter carriers.

 
Limitations

• Bad weather may ground aviation.
• Lack of waterborne landing craft prevents any other means of assault.
• Helo assault is limited to troops and light cargo.  Heavy equipment, tanks, armored vehicles, etc. cannot be transported by air.
• Helos are extremely vulnerable to even modest anti-air defenses.
• Helo carriers have very limited wave transport capacity.  For example, 20 helos per wave x 15-20 troops per helo = 300-400 troops per wave and that’s just troops, no equipment.  It would require 5-7 waves, over many hours or multiple days, to get the full troop complement ashore and that assumes no helo attrition.  The reality is that any reasonable helo attrition would likely result in a portion of the troops never getting ashore and certainly not in a timely manner.
• Limited by the need/availability of suitable cleared landing sites; such sites can be reasonably anticipated by the enemy and become fire traps as demonstrated in Vietnam.

 
Sustainment

The original Marine leadership was focused on division level assaults.  What they failed to address was sustainment.  While simply moving troops ashore is easy (ignoring the extreme vulnerability of the helicopter and the potential lack of suitable landing sites), sustainment via helicopter is not.  In fact, it is impossible.  The logistic supply demands of a division in combat are staggeringly huge and the cargo carrying capacity of a helicopter is vanishingly small.  This remains an unexplained – and hand waved away – weakness in today’s various vertical assault concepts (helos, MV-22, well deck-less LHAs, etc.) as well as the Commandant’s dispersed, hidden, platoon size missile shooters concept.  It is not possible to sustain an assault using helicopters.
 
 
Summary
  
The original rationale for the LPH and vertical assault was dispersal due to the threat of atomic weapons.  As, discussed, this is no longer a valid concern.
 
It is noteworthy that the original Marines identified significant weaknesses in the concept including the extreme vulnerability of helos to anti-air defenses and the absence of waterborne landing craft as an alternative.  Other weaknesses included the inability to transport heavy equipment, the limited number of troops that can be transported per wave, and the impossibility of sustaining an assault using vertical transport.
 
We see, then, that vertical assault is an inherently flawed concept that was justified only by the extreme atomic threat.  With no realistic atomic threat today, one has to ask why we’re still pursuing the flawed vertical assault concept?
 
Where does this leave us today?  For starters, we’ve begun repeating the original mistakes such as the absence of waterborne landing craft in the early variants of the America class LHA.  Additional problems include the extreme vulnerability of vertical landing aircraft to anti-air defenses, first noted by the Marines back in the original concept development.  In fact, the threat to helos has increased markedly over the years with the advent of small, portable, shoulder launched, heat seeking, anti-air missiles of the Stinger type.  Vertical landing aircraft are simply not survivable over a defended battlefield as has been repeatedly demonstrated in the real world (Vietnam, Soviet Afghanistan, US Afghanistan, etc.).
 
The inability to transport heavy equipment by air continues, today, and is a serious weakness in the concept.  This limitation relegates any assault to a light infantry effort only and makes the enormous cost and resources dedicated to such a limited capability highly questionable.
 
The need for secure, cleared landing sites has only gotten substantially worse with the advent of the MV-22 which requires enormous cleared areas and huge separations between aircraft to the point that a massed assault is simply not possible.  Landings will have to be a very slow, one-at-a-time affair that is ideal for enemy defensive fire sequentially focused on each landing aircraft in turn.
 
Despite clearly and correctly identifying the inherent flaws in the vertical assault concept, Marine leadership pushed ahead with vertical assault in the belief that the atomic threat was more significant than the known weaknesses.  One can only speculate whether the Marines would have adopted vertical assault if there had been no perceived atomic threat.
 
With no realistic atomic threat today, one has to ask why we’re pursuing an inherently flawed concept?
 
Worse, we have taken the concept and reduced it from a full, divisional level effort and capability to a light infantry effort with no supporting tanks, armor, artillery, heavy mortars, or mobile anti-air vehicles.  Is the staggering cost to build and operate 30+ amphibious ships worthwhile to deliver light infantry ashore?
 
It would seem that vertical amphibious assault is an example of inertia.  The helo assault was established and continues just because it exists.  It exists because it exists.  We need to re-examine this 1940’s era concept in light of the known flaws and, especially, modern defenses which have rendered helos even more vulnerable than they were originally.  The cost/risk to benefit ratio does not support continued vertical assault.
 
 
 
___________________________

 
[1]Norman Friedman, “U.S. Aircraft Carriers, An Illustrated Design History”, Naval Institute Press, Annapolis, MD, 1983, p.359-370.