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Background  —  Sealifter Comparisons — Landing Craft, Air Cushion

LCAC underway loaded with M60 tank and trailer The LCAC  – “... Fair is foul, and foul is fair: Hover through the fog and filthy air.”
LCAC stopped on water surface - note Bison-like LAV-25 The US Navy’s ‘Landing Craft, Air Cushion’ is a radical approach to delivering Marine Corps amphibious assault forces ashore. Relevant to the development of the San Antonio LPD , the advantages of hovercraft LCACs are obvious. As air-cushioned vehicles,  LCACs are able to deliver troops, vehicles, and equipment over a beach, not just onto it. A less obvious benefit is that LCACs can simple glide off of an LPD’s well deck ramp (the well deck must be flooded to launch conventional landing craft). ‘Beach’ may also be a misnomer. The LCAC can operate just as easily over snow or ice, mud flats, riverine estuaries, etc – in fact, virtually any relatively level terrain can be used.

LCAC loaded with Humvees - DOD photo LCACs to “...run ’em ashore...”
The US Navy ran an experiment with air-cushioned landing craft in 1977.  Having shown that the hovercraft  reduced  congestion on landing beaches,  the LCAC was ordered into production [1], the first LCAC was delivered to the US Navy in  December 1984.

  Dimensions:   26.8m long x 14.3m beam x 0m draught
  Displacement:   200 tons  (full load)
  Propulsion:   4 x 12,280bhp Avco-Lycoming turbines,
    2 x reversible propellers plus 4 x lift fans
  Carrying capacity:   60 tons  (75 tons overload)
  Vehicle capacity:   12 x Hummers, 4 x LAVs (or 5t), 1 x tank
  Speed / range:   74km/h / 485km @ 65km/h (with payload)
  Crew / armament   Five / 2 x 12.7mm M2HB (or 40mm AGLs)

LCAC ramp with HMMWVs Tracked LAVs reloading - US Navy photo The LCAC became fully operational in 1987 and the type was involved in the 1991 Gulf War. LCACs had been tested earlier in tropical and in Arctic conditions.  Trials in Alaska showed that, while LCACs could handle thin ice and calm water, higher sea states, intense cold, and icing-up conspired to limit operational effectiveness. [2]

5t truck and 155mm howitzer unloading LCAC underway with two 5tons - US Navy photo “... They were all left behind on the beach ...”
Outside of the arctic environment, the LCACs performed well. In any case, the San Antonios (like most LPDs) aren’t ice-capable ships. The emphasis is on overseas CF deployments into warmer climes. For such deployments, LCACs will offer greater flexibility than a conventional landing craft. That the preferred San Antonios were tailored for LCACs is also an advantage.

Also seeJoint Support Ship.  The JSS Project is distinct from the Amphibious Assault Ship but the two are related  (at least by budget).

[1] Designed by Bell Aerospace Textron, the LCACs were built by Textron Marine and Land Systems and Lockheed. A SLEP (Service Life Extension Project) is now underway for the LCAC fleet (adding 10 years of service life to 74 LCACs). It is unlikely that the US Navy will be willing (or able) to spare LCACs, and an eventual replacement is at a very early planning stage. DND is, therefore, in the position of either ordering new LCACs or designing its own equivalent air-cushion landing craft  –  perhaps in cooperation with the Canadian Coast Guard?
[2] There are other limitations to air cushion vehicles as landing craft  –  the high operating costs (incurred through the use of gas turbine engines), excessive propeller noise which can be heard from miles away (a distinct tactical disavantage when approaching hostile shores).