There are probably more kinds of amphibs than any other sort of military ship except the broad category "naval auxiliaries." They have many different functions. They achieve these goals by different means. The biggest "professional" amphibs are the aircraft carrier types: LPH, LHA. LHD. These tend to carry a significant combined arms team including heavy tanks, mechanized infantry, artillery, support troops, an airmobile light infantry element, the ability to move some medium equipment airmobile, and often some strike aircraft (gunships and VTOL Harrier jets). These ships carry one or two battalion combat teams, as a rule, including organic air assets. They can cross oceans and serve as flagships, and they were designed to provide some naval gunfire support (although this was not significant, and the capability has been removed from most). The medium sized "professional" amphibs are LSDs, LPDs, LSTs, and similar vessels. [The US Army has LSTs, but does not call them by that designation]. These vessels are more specialized. They tend to focus on carrying and delivering tanks and heavy and medium vehicles, either by beaching directly or by using landing craft or LCAC air cushion vehicles. They usually carry one or two helicopters, or have a helicopter platform. US amphibious forces combine one big LHA or LHD with about three LSD/LPDs. This can deliver a brigade - for example the Third Marine Expeditionary Brigade on Okinawa is the principle offensive land unit of the Third Marine Division and the Pacific Command. Small professional amphibs include LSMs (think baby LSTs) and specialized support vessels based on their hulls. For example, in WWII the USN had LSMRs, -LSMs fitted with rockets for bombardment. This class of amphib is more suitable for short range operations, and it is the primary kind of Chinese amphib. It is really better to have more baskets than all your eggs in one, so many little ships are more likely to deliver your troops than a few larger ones. We use big ships because we have to cross oceans. China uses small ships because it only has to cross 81-110 miles of sea. A smaller kind of amphib exists - landing craft. These are great for short range operations, and "short range" can be significant. Israel did a raid on LCMs that transited a long distance. Japan used to do the same thing. Chinese LCMs can operate for 10 days at sea. These craft can turn merchant ships into amphibious ones, so they are popular. They also are cheap. The "amateur" kind of amphib is the merchant ship. Give a merchant ship landing craft and you have a troopship (APA) or an amphibious cargo ship (AKA) - well that was the old terminology. Now it is LPA and LKA. Merchant ships can carry significant weapons - to provide fire support. They can carry landing craft ready to launch - see a barge carrier and the semisubmersable heavy lift ship. Amateur amphibs in wartime carry most of the invasion forces. Britain had so many merchants in the Falklands war that one military friend of mine observed they could win the war entirely with merchant ships! Related ships are not true amphibs - for example ferryboats. They need a dock - but are still useful - particularly for getting units with lots of vehicles mated with their vehciles aagain.

Take a closer look at the details. Ask yourself, what are the differences between each ship? What does one do that the other doesn't? How many landing craft of what types? How much cargo? How many troops? Helicopters? USMC amphibious units are based around the Amphibious Ready Group (ARG). Each ARG is much smaller than it used to be in terms of numbers of ships, usually consisting of one aviation ship (LHA or LHD) which can land assault elements by helicopter or sea, one Landing Ship Dock (LSD) and one Landing Platform Dock (LPD). More or fewer ships may be employed though as the situation dictates. This represents a considerable reduction in the numbers of different types of ships needed to carry the same sized force over earlier incarnations, so what you see as a large number of similar ships isn't really that far off - these have replaced far larger numbers of very dissimilar ships. This is because the variety of roles has been combined into fewer but larger, multi-purpose ship types. The LHA's or LHD's form the centerpiece of the ARG. The Tarawa class LHA's represent the older LHA type. The LHA combined the characteristics of the LPH, or Landing Platform Helicopter of the Iwo Jima class with the LPD (see below). The LPH carried no landing craft, only helicopters so that it could not land heavy equipment nor could it land troops in bad weather. The LPD carried some landing craft and a lot of troops and heavy equipment but no permanent aviation capacity. Combining the features of these two different types into one reduces the number of ships necessary to transport the landing force and improves flexibility (assaults can still be made by sea if weather prevents flying for example). The Wasp class LHD is an improved version with better facilities for LCAC air cushion landing craft, which were designed after the LHA. These ships are designed to act as the flagships for the ARG while delivering troops and equipment to shore either by landing craft or helicopter (or both). A Wasp class LHD can carry 3 LCAC and has 100,000sq ft for cargo, 20,000 sq ft for vehicle stowage. The older Tarawa can carry 1 LCAC plus various combinations of conventional landing craft, 30,000 sq ft of vehicles, 42 CH-46 or 28 CH-53 helicopters. The LSD dates back to WWII and was designed principally to carry a lot of landing craft that could be launched quickly (pre-loaded) through a well-deck in the stern. It is the only of the 3 major types of amphibious ship in the USN that survives from its original WWII origins. LPD's are similar to LSD's (in some cases using the same hull) but trade off landing craft capacity (LCAC's) for additional cargo and troop capacity - for example, only 2 LCAC are carried in the LPD instead of 4 in the LSD. The LPD was concieved as a replacement for the eariler APA (which carried personnel) and the AKA (which carried cargo). Unlike the LSD, there is a permanent flight deck installed above the docking well and the well in permanently enclosed, allowing the loading of landing craft even in poor weather. Helicopters from the LHA/LHD can land and pick up troops from the LSD while the LCAC's deliver heavy cargo to the beach. Each ARG carries a Marine Expeditionary Unit (MEU) which will contain a variety of elements usualling including several Battalion Landing Teams (BLT) plus support and aviation elements, including if needed a flight of AV-8B Harrier II's operating in the CAS role from the LHA/LHD. The composition is flexible according to role so don't ask for anything more specific. 2nd and lower rank navies around the world still use lesser makes of amphibious assault ship. The LST is the most common, a few of the vast numbers (over 1,000) built during WWII still surviving in Asia. The LST is designed primarily to disgorge cargo by driving up onto the beach and opening up its massive bow-doors to dispense its contents. It can't carry very much doing that though so they usually land some of their troops/cargo first by landing craft - typically 4 or sometimes 6 LCVP's. In other words, the LST can carry about 1 company sized unit in an assault role. In other words it takes A LOT of LST's to land a force of reasonable size. But they are cheap to build and operate and adequate for smaller users. The LST fell out of favor in the west decades ago due to its low speed, and limited capacity. Elcid mentioned the LSM. These were developed by the USN in 1944 and abandoned as grossly inefficient about 1946. They somewhat resemble small LST's including all of that types deficiencies plus many more. They are principally found only in the 3rd world, and usually as cargo-haulers because internal infrastructures are so poor, not as amphibious assault craft. In spite of this, Elcid is under the impression that China is going to take over the world with a vast fleet of these flimsy little craft. Pretty much everything else falls under the heading of "minor craft", i

Alright, but can you tell me the differences between all the different "big" amphib ships still in the USN? ie Amphibious Transport Docks, Amphibious Assault Ships, Dock Landing Ships?

I already told you. The LHA/LHD type ships look like aircraft carriers, and carry a significant air group. This means they can support significant airmobile operations (a battalion combat team) or they can carry significant strike aircraft (Harriers) with a smaller airmobile capability. They also can land a heavy or medium mechanized battalion from landing craft or skimmers. Finally, they are significant flagships and have major communications facilities, which matters. The smaller ships left are essentially similar - LSD and LPD are ships with docks - they flood and sink partially and launch landing craft out the stern doors. They carry few troops and are vehicle oriented. These ships are important for increasing the heavy punch of an amphibious brigade. They do have helicopter platforms, or even hangers, but do not operate significant numbers of aircraft. Instead, they use their flight decks for lots of minor functions - replenishment - search and rescue - sending small airmobile elements (which can combine with those from other ships) - medevac - sending critical supplies to forces ashore - many tasks. The LSTs are gone from active service, but some remain in reserve units. These can land over the beach.

"Alright, but can you tell me the differences between all the different "big" amphib ships still in the USN?" "ie Amphibious Transport Docks, Amphibious Assault Ships, Dock Landing Ships?" There are essentially only 3 basic types and I already described them in detail. LHA's and LHD's combine the functions of helicopter and seaborne assault by featuring large flight decks and hangars for helicopters plus a stern docking well for landing craft combined with significant troop and cargo capacity. LSD's provide the bulk of the landing craft capacity with a significant troop and cargo carrying capacity but no permanent airborne element (no hangars for helicopters). LPD's look like LSD's but trade off space in the docking well (landing craft capacity) for cargo and troop capacity. Now read my original post again, study the links I provided and come back when you're paying more attention.

My question/concern is with the increasing size and capacity of the post WWII amphibious ships. Increasing size and capacity may lead to certain efficiencies of scale but the loss of a single ship leads to the loss of considerable amounts of men and material plus the complexity of the ships does not allow for rapid building of additional new ships or replacements. I wonder if economic efficiency has got the better of war fighting efficiency.  

You concern is valid, HOWEVER, it may be irrelevant....IF future combat is of the type Desert Storm/OIF or short-term combat between the PRC and the US-short-term because nuclear weapons ARE used or short-term because combat is limited for FEAR of nuclear weapons use, THEN the ability to rapidly construct large numbers of weapons is irrelevant.  In short, if the next war(s) are Desert Storm rather than WWII it doesn't matter if we can build 1,000 LST's or not.

Let me clarify my statement. I see a distinction between cargo type ships that are designed to dock at a secure port to roll off men and material after an uncontested voyage, as in the preparation for a Desert Storm /OIF and what many consider to be ships designed for amphibious warfare where troops and equipment are transpoerted to a frontline shore through contested waters. If it is believed that the latter scenario is extremely unlikely than the economies of the larger ships are preferable. I am somewhat concerned that the government has become somewhat complacent because of our historical air and sea dominance.