What did Germany do to defend Omaha Beach on D-Day?

After the Germans had successfully invaded and occupied France, they set about fortifying the coastline along the English channel, especially the area of the coast where they thought an Allied forces invasion might take place. That area is called Normandy.

The first projects involved basic beach defenses, with machine gun and mortar positions being dug in to the over looking hills and cliffs. Larger and much better protected concrete bunkers and heavy caliber gun sites were built later.

Each position was sited to give maximum inter-locking fire patterns, so that each position could support those around it. The positions were also laid out in staggered lines that were from 500 to 3000 yards deep. Anti tank ditches were dug that were so wide and deep that it was impossible for armored vehicles to cross them. Hundreds of thousands of buried explosive mines were set out in front of the main defense lines, to blow up either individual soldiers or vehicles.

Large caliber guns, capable of firing as much as 12 - 15 miles / 20 - 25 Km out to sea, were designed to attack and sink the ships that would be used in a invasion from the water. These were implaced in reinforced concrete bunkers with walls up to ten feet thick. Such gun sites could only be destroyed by direct gun fire from off shore naval vessels , firing at point blank range. Or by placing explosive charges directly in the gun ports, but daring, attacking soldiers who had come ashore from the landing craft.

The above fortifications were built by the Germans over a 4 year period, and they had the time and the expertise to design a really complicated set of defenses. The Allies also had the time to figure out how to defeat the defenses and how to get through them. It was through a combination of specialized armored vehicles, new tactics of combined arms fighting, and the use of mass parachute landings, behind the defensive lines, that turned the battle for the winning cause.

I notice that you asked about "Omaha" beach only. Please remember that on June 6th, 1944 the landing operations were carried out by three armies, only one of which was American. The USA was a part of a "team" of nations that worked together, to eventually defeat the Nazis. The other nations were the United Kingdom, and Canada. Each has it's own series of beaches to attack, all code named differently. Omaha was one of many beaches in the D-Day operation.