All the landing ships I’ve seen open from the front, and that’s never made sense to me considering that a good machine gun volley could take down the soldiers before they even have time to react. If they opened from the rear they would at least provide some protection and a place to retreat if need be. Are there any rear-opening ones? Why do most open from the front?
What if there was a sharp drop off (like at most beaches)? The landing squads already are in deep enough water when you consider all the equipment they carried.
My guess would be that it’s done that way so that the deploying soldier isn’t required to swim while carrying a weapon and full battle gear. Rather, get out and spread out asap instead of immediately sink to the bottom.
Of course, that’s a wild-ass-guess. Your mileage may very. Ask a doctor before considering anything I might say as being factual.
If you ever had to exit one with a full combat load, you’d want to do it at the shallower end. Machine gunning is a horrific death, but I don’t think I’d want to drown or be crushed by my own (retreating) landing craft.
The modern USMC is fond of using hovercraft for amphibious landings, a major plus being that your men are perfectly dry when they hit the beach.
So do those have doors in the back?
It’s logically placed, by necessity. As you can see from the diagram in the wallpaper of this page, the Higgins Boat was designed to run up the beach, and then when it was planted, it dropped its ass-end slightly deeper into the water so that it could pull itself back off. This was a critical feature, as there would be hundreds more boats behind it waiting to land.
My guess is that would be part of the reason why the LCVP didn’t come with fancy features such as detachable nosecones or side-opening ramps. A front opening ramp, even if it can’t be closed, won’t prevent a Higgins Boat from pulling itself (or being towed) back off the beach, even if it is just in order for it to scuttle itself in deeper water. It also has a ramp “footprint” exactly as large as the beam of the boat, so they can land right next to one another.
You can’t go out the back because soldiers would find themselves in deep water behind a line of boats which all want to back up and get the fuck out of there, not to mention the dangers of being crushed between boats while advancing to the beach. And just imagine what would happen if a dozen boats with side-opening ramps hit the beach all at the same time, without enough clearance to drop the ramps. Not pretty.
The landing vehicles the USMC uses have rear doors. They open once the vehicle is out of the water or can be used to go inland some ways and operate like Armored Personnel Carriers (APCs, the M113 is a common example).
Obviously, jumping off in deep water with a lot of gear is unhealthy. But also consider that bobbing in the water (assuming you had floatation devices) leaves you more vulnerable to being picked off by the OP’s machine gun bursts than if you hit the beach and run for cover.
The concept today tends more towards landing on a beach that is either lightly held or not defended directly at all, rather than the Normandy type storming-the-gates-of-fire approach. Hovercraft and helicopters make it possible to go to landing sites that old WW2 landing craft couldn’t access or land at.
Were we to try to sieze the French coasts from some notional occupying power now, rather than dive right into the lion’s mouth, we’d likely “vertically envelop” tactially advantageous ground near a major port and support the heliborne assault with heavy vehicles like tanks and APCs brought in over rocky shores or “impassable” wetlands via hovercraft. The initial assault would be much faster and much more in depth. Reinforcement for the initial force would then occur via landing ships over beaches that had been secured from behind and/or above.
Amtracs, or Ampibious Tractors, beginning with the LVT-1 in 1941, are smaller landing vehicles with tracks (Landing Vehicle Tracked), and rear-opening doors. These vehicles swam to the shore and drove up onto it, then the Marines aboard could get out the back and use it for cover until they pressed on, or they could ride in it to their objective. They were slower and smaller than the Higgins Boats, and more expensive, I believe. In a massive war, you need cheap stuff that works and get things done fast, because there are a lot of them coming up behind you fast.
The current USMC model is the AAVP7A1.
The LCAC’s (hovercraft), have the ability to spin on a dime, so door placement is less critical, it can be easily oriented any direction. But the LCAC’s (Landing Craft Air Cushioned) tend to bring in things like tanks and heavier equipment, not just trigger pullers.
Ah, the mystique that surrounds the armed forces.
I used to like the MAGTF demonstrations at the MCAS El Toro airshows. Helicopters, tanks, OV-10s dropping troops out the back, fire, smoke, explosions…
All long gone from my local area now that El Toro is closed. 
This statement was not intended to belittle the infantry man at all. This is merely a statement that personnel can arrive over the beach in a number of ways that heavier equipment cannot. Tanks are not brought in by helicopter, for instance.
And MAGTF (Marine Air Ground Task Force) demos kick some serious ass!
Some WWII landing craft, such as the LCIs, had a conventional bow, and a pair of ramps, one to either side, for disembarking. Needless to say, this creates a couple of choke-points where everyone in the craft has to line-up, slowing the whole ‘hit the beach’ process way the hell down. Examine the LCI (Landing Craft, Infantry) in the foreground of this illustration. You’ll clearly see the disembarkation ramp (in it’s stowed or ‘retracted’ position) and a conventional bow.
The advantage of a bow ramp is not only that it gets you closer to the beach, but that it allows you to get more people off the boat, faster.