Maybe my thoughts are inaccurate because I’m basing this off movies and and documentaries, but the amphibious landing vehicles had a front folding door allowing all soldiers to be slaughtered by targeted machine guns. Pre-944 Amphibious landlings in the pacific canpaign that had vehicles with armor plated stationary machine guns and soldiers exited from the side of the vehicle requiring Japanese machine gun nests to rotate their aiming instead of stationary fire down soldiers directly facing them in a single line.
Also why couldn’t they all just be dropped directly behind the beach heads? I know they did (Band of Brothers). But why not also right behind the beach heads? Anti air guns I assume but maybe at night using gliders?
In regards to the airborne operations, dropping paratroopers close to the forward defenses would be an invitation to have a lot of drowned men, given the proximity to the beach. In reality, the confusion of the night operation already resulted in a scattered drop and caused the airborne forces to miss their objectives. Had the DZ been situated closer, some of the soldiers would have landed in the channel and not the French countryside.
Second, the airborne forces had a more vital role to play in Operation Overlord than just assisting landing forces destroy the forward defenses. American paratroops were tasked with isolating the amphibious landing zone from German counterattack, buying enough time for the invasion to gain a solid foothold on the continent. If the airborne forces were used to attack the beach defenses, the allies would have had a greater risk of being destroyed by a counterattack.
A beach landing is against a prepared and present enemy was and is a dangerous thing. Getting bogged down on the beach in the enemy-designed killing zone is the main danger, and you need to get out of that killing zone as soon as possible.
The system with a landing ship with a frontal exit allowed for the troops to disembark quickly and begin advancing out of the killing zone. With a side-exit system, you face the danger of troops taking cover behind the doors and not advancing, which would not only keep them in the enemy-designed killing zone, it would also make it harder for the landing craft to return to the troop ship to embark the next wave of troops.
The Western Allies knew that the Germans had some 50 divisions in France and that there were several armoured divisions in the German reserve in the west - they knew they needed to get a lot of troops and equipment ashore, and get the planned Mulberry harbours online to provide those troops with reinforcements, ammunition and supply to resist the expected German counter-attack. If the beaches were lost, the Western Allies would not be able to support the troops.
D-day was a remarkably successful operation. Despite the paratroopers being scattered over half for the Cotentin peninsula and the much-depicted problems on Omaha beach, where the bombers had missed much of the defences and the Germans had a full division on the beach, the Western Allies suffered only about 10 000 casualties (of which about 4 100 dead) on the first day, of the 160 000 troops landed. 2 000 of those were suffered on Omaha beach.
As a comparison, Utah had 197 casualties, Pointe du Hoc 135, Gold 1 000, Juno 961 and Sword about 1 000.
The Western Allied air transport capacity was stretched to the limit to deliver the two American (82nd and 101st) and single British (6th) airborne divisions, plus the commandos and other special troops by air and then supply them - there were no more planes to transport more troops to Normandy or supply them.
Paratroopers are light infantry - they have little to no artillery or AT (and what exists are light guns), no tanks, no motorised transport and their supply will be iffy at any time. It was not possible to have the paratroopers take the beaches from behind. Without the frontal attack by regular forces supported by heavy naval artillery, the paratroopers would have been isolated and eventually destroyed by superior German forces.
Can I add gliders to this list?