Why weren't Marines chosen for Normandy?

Without reading other comments, I'm guessing: The large scale of the event?

Just my immediate thought, the marines were already heavily entrenched in the pacific theater

It may be a simple case that the Marine Corps Is in the department of the Navy.
The Navy got both the Army and Marines ashore. The Navy was the artillery and cover for both the Army and Marines
In Europe the naval guns could reach only so far.
In the Pacific, the Navy was continual artillery and cover.
Did i miss the part where the Marines are part of the Department of the Navy

I've read as much of this thread while quietly screaming inside. There are many misconceptions and failures of historical accuracy going on. I'm just going to throw some random facts out and then duck.

Amphibious warfare doctrine was developed as a joint Department of War (Army)/Department of Navy (Marines) endeavor in the 1930s, when a future need was perceived. Each Amphibious Corps was to be composed of an Army division and a Marine division. You can even find the FM 34-something online if you look hard enough, but since the question says not to google, I can't get super accurate.

At the start of the war, there was the Pacific Amphibious Corps (2nd MarDiv and 3rd Infantry Division) and the Atlantic Amphibious Corps (1st MarDiv, 1st Infantry Division). Organized per the amphibious operation doctrine outlined in the 30s.

Some say it was an urgent need for manpower by the Navy in the Pacific, others say it was because Marshall didn't want any Marines in the ETO/MTO, but very quickly, the 1st MarDiv was transferred to the PAC, and the 3rd Infantry Division was sent to the AAC. Someone may or may not have recorded some Army General saying something to the effect of "if there is one Marine within a thousand miles of Berlin, all we will hear about is how the USMC singlehanded defeated Hitler". Given the USMCs proclivity for PR grandstanding, that might not have been an unreasonable assessment.

The 1930s Amphibious doctrine quickly broke down and the Army formed it's own school to train divisions in Amphibious warfare in Virginia. They moved about six divisions through them before closing it down in late 1943-ish.

It was not until 1957 that the Army stoped training units in amphibious warfare and ceded that mission the the USMC. In 1944, both branches were equally trained and able to conduct amphibious operations, and both did.

At the time of Normandy, there were only four Marine divisions -- the 5th Marines had been formed, but were not yet trained and would not be combat ready until 1945. The 6th Marines were formed three months after the Normandy invasion. All of those four divisions were assigned to the PTO. Only US Navy ships companies had any Marines in theater, who were neither trained to assault said beach, nor had equipment to assault said beach, and were very few in number.

Planning traffic to those five beaches had been painstakingly done over the previous two years. The US Army put in an Army -- three divisions on the beach, two Airborne. The British Army did the same. You had another almost Army sized force made up of Canadians, ANZAC, Dutch, Norwegian, Polish, Czech, Greek and French troops operating in the area as well. An extra platoon of Marines from the USS Texas is not going to make a difference if three Armies can't cope with it, all they are going to do is disrupt traffic going onto the beaches and get in the way. The only person that every seriously considered committing the ships company of the USS Texas was the ex-Marine that authored that article that was much cited throughout this thread. They were untrained, unequipped, and there was no reason to throw a wrench into a plan that was working.

I'm going to duck now, feeling like I've pissed off the Army and Marine readers alike. Cheers y'all.

Other the Marines assigned to the Office of Strategic Services there were no Marines assigned to Europe!

The Marines were chosen at Normandy. Marine officers did a lot of the planning for Overlord. The Marine Corps developed the Higgins Boat. Marines trained and prepped the Army units designated to go ashore in Amphibious assaults, and Marine riflemen cleared the path for the invasion fleet by detonating mines. No sense rotating 1st MarDiv out from the Pacific to go put a boot up Hitler's ass when the Army has plenty of units in place that can stick the pointy end in, so send the officers and enlisted men with the experience and know how needed to ensure they get the job done right.

Simple. The USMC was engaged in the Pacific Theater, and the majority of Army assets were deployed to the European Theater. Given the scale of the Utah and Omaha landings, there would not have been sufficient USMC assets available to be pulled from the Pacific and deployed to England. The Army already had more than enough amphibious landing experience with North Africa, Sicily, and Italy to carry out the Normandy Invasion.

Maybe because their plate was over full in the Pacific theater!

The different departments at the High Command in Washington thougt that Marines would be used only in the Pacific. The service group always found that a mix of Marines and Army personnel would create a problem for the commands of unit because of chain commands of different types of training.

It was decided that the Pacific was a Navy show (Nimitz). Army units like my Grandpa's came in to relieve Marines as they island hopped.
Europe was an Army show. Much smaller naval assets employed. England and Italy became "Carriers".
Japan projected power through its navy and naval infantry. There was no German fleet to threaten us directly.
Maybe a bit of traditional vengeance? PH being a navy attack on our navy?