There was one person in charge of the Allied invasion of Europe and subsequent campaign to defeat Nazi Germany: General Dwight Eisenhower, Supreme Commander, Allied Expeditionary Forces. All Allied military forces came under his command with an occasional exception. Most important, Eisenhower was backed by three key men: Army Chief of Staff George Marshall, US President Franklin Roosevelt, and British Prime Minister Winston Churchill. When he had to flex his muscles to bring subordinates into line, he had a lot of muscle behind him.
The Germans, who have a reputation as organized and efficient, had a command structure resembling a bowl of spaghetti thrown against a wall. In a report written for the Allies after the war and published in a fascinating volume, Fighting the Invasion: the German Army at D-Day, General Günther Blumentritt, who served as Chief of Staff to Herr General Feldmarschal Gerd von Rundstedt, Oberbefehlshaber West or ‘OB West’ (C-in-C West), wrote about the command structure which I have summarized below.
OB West reported to OKW (Oberkommando der Wehrmacht or German Armed Forces High Command), which had operational responsibility for war on the Western Front. Subordinated to OB West were Army Groups B and G which controlled all subordinate German Army forces in France, Belgium, and the Netherlands. (The Military Governor of France and the Military Governor of N.France/Belgium, which had their own special units and security troops, reported directly to OKW.)
However, OB West only had authority over German troops in France, Belgium, and Holland as it regarded coastal defense. Only if an actual invasion occurred, would the German Army commanders in Belgium and France be completely subordinated to OB West. The German Army commander in the Netherlands did not come under the authority of OB West in the event of invasion. He reported directly to OKW. However, the majority of front line German Army combat units in Holland came under the command of Army Group B and not the German Army commander in Holland.
The Germans had a shortage of troops but not of Field Marshals. Rommel (seen above on right), the unbeatable Desert Fox, was sitting around in Germany while the unbeatable German Afrika Korps was being beaten – and later surrendered to the British 8th Army. (Eventually, the entire Deutsche Afrika Korps ended up as POWs in the United States.) So Hitler sent Herr General Feldmarschal Rommel to France to assume command of Army Group B, which already reported to Herr General Feldmarschal von Rundstedt (seen above on left) in his capacity as OB West. So theoretically Rommel was subordinated to von Rundstedt but all German Field Marshals had the right to contact Hitler directly so it wasn’t clear that Rommel really was subordinate to von Rundstedt and both of them gave orders to Army Group B and these orders often conflicted.