What is the birthday of the Navy?

The correct answer is the date that marks the establishment of the Continental Navy, which occurred on October 13, 1775. This date is celebrated as the birthday of the United States Navy because it represents the formal decision by the Continental Congress to create a naval force to combat British maritime power during the American Revolutionary War. The establishment was an important step in the development of a naval tradition and played a crucial role in ensuring the success of American independence.

The other options reflect significant dates in American history, but they do not specifically correspond to the founding of the Navy. For instance, January 1, 1775, does not have a connection to naval establishment; July 4, 1776, marks the adoption of the Declaration of Independence; and April 21, 1783, is referenced with respect to the end of the Revolutionary War but is not associated with the Navy's creation. Thus, October 13, 1775, stands out as the definitive birthday of the Navy.