Final answer:
The ultimate tactical control of all Reaction Forces as per the United States Constitution rests with the President, who is the Commander in Chief of the Army and Navy, overriding specific commanding positions within military branches.
Step-by-step explanation:
The question "Who has tactical control of all Reaction Forces?" relates to military command structure and authority. Historically, notable figures like Admiral Chester Nimitz, who was the Commander of the US Pacific fleet during World War II and later accepted the surrender of Japanese forces aboard the USS Missouri, and Douglas MacArthur, who commanded US forces in the southwest Pacific, had significant tactical control over their respective forces during wartime.
However, according to Section 2 of the United States Constitution, the President shall be the Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into actual service. Therefore, while specific positions such as Commander in Chief, U.S. Pacific Fleet or Commander, Naval Surface Force Atlantic may have operational or tactical control, the ultimate authority rests with the President.