This key video is a long talk about German defenses. Guns pointed down the length of the beach, not out to sea. Does "guns" includes machine guns? Ehh .. See 2.2. A lot of casualties were caused by the various types of artillery, supplemented by machine guns.

They say a picture is worth a thousand words. There is a picture out there showing a smaller-calibre artillery gun I believe on Omaha Beach. It is in a simple slit trench on a bluff, no top cover, and it can shoot out the open end of the slit trench. The slit trench is at an angle so that it can shoot down the beach. You can not see the position, let alone shoot at it, if you are facing south.
 

It's well known that the duplex drive tanks had a disastrous time trying to land. However, the wading tanks later did better. The wading tanks were released from their landing craft (varying sizes) in shallow water. By the way, I've never seen these tanks in Saving Private Ryan.

Unsurprisingly, they did have (ginger?) seasickness pills (source, if you care).

Before D-Day, the Americans were not aware of certain things:
Omaha Beach had been reinforced with the experienced 352nd infantry division.
Pointe du Hoc didn't have any artillery. The Americans therefore launched troops and tanks farther from shore.
Before D-Day, the British had found from experience that duplex drive tanks are likely to sink in choppy water. On D-Day they launched their tanks closer to shore. The Americans did not learn this lesson.