On Precedence and Seniority

As part of this post, RobertaX makes the following statement in a parenthetical footnote:

2. No, I'm guessing. But the USN is the Senior Service, after all.

In her comments section I observed that this wasn't actually true. Since I think her subsequent comment a bit ambiguous, I offer the following excerpts from the wikipedia pages for both the US Army and Navy

The United States Army is the branch of the United States armed forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military and is one of seven uniformed services. The modern Army has its roots in the Continental Army which was formed on 14 June 1775,[1] before the establishment of the United States, to meet the demands of the American Revolutionary War. Congress created the United States Army on 14 June 1784 after the end of the war to replace the disbanded Continental Army. The Army considers itself to be descended from the Continental Army and thus dates its inception from the origins of that force.

Congress formally authorized creation of the Continental Army more than a year prior to the actual Declaration of Independence. Congress formally replaced the Continental Army with the United States Army on 14 June 1784.

The US Navy wikipedia page is composed quite differently to that for the Army, so the quotes are more extensive:

In the early stages of the American Revolutionary War, the establishment of an official navy was an issue of debate among the members of the Continental Congress. Supporters argued that a navy would protect shipping, defend the coast, and make it easier to seek out support from foreign countries. Detractors countered that challenging the British Royal Navy, then the world's preeminent naval power, was a foolish undertaking.[5]

Commander in Chief George Washington commissioned seven ocean-going cruisers to interdict British supply ships, and reported the captures to the Congress. This effectively ended the debate in Congress as to whether or not to "provoke" the British by establishing a Navy as Washington's ships had already captured British ships, somewhat a provocation.

While Congress deliberated, it received word that two unarmed British supply ships from England were heading towards Quebec without escort. A plan was drawn up to intercept the ships—however, the armed vessels to be used were owned not by Congress, but by individual colonies. Of greater significance, then, was an additional plan to equip two ships that would operate under the direct authority of Congress to capture British supply ships. This was not carried out until 13 October 1775, when George Washington announced that he had taken command of three armed schooners under Continental authority to intercept any British supply ships near Massachusetts. With the revelation that vessels were already sailing under Continental control, the decision to add two more was made easier;[9] the resolution was adopted and 13 October would later become known as the U.S. Navy's official birthday.[10]

The Continental Navy achieved mixed results; it was successful in a number of engagements and raided many British merchant vessels, but it lost 24 of its vessels[11] and at one point was reduced to two in active service.[12] As Congress turned its attention after the conflict towards securing the western border of the new United States, a standing navy was considered to be dispensable because of its high operating costs and its limited number of roles.

The United States would be without a navy for nearly a decade—a state of affairs that exposed its merchant ships to a series of attacks by Barbary pirates. The sole armed maritime presence between 1790 and the launching of the U.S. Navy's first warships in 1797 was the U.S. Revenue Cutter Service (USRCS), the primary "ancestor" of the U.S. Coast Guard. Although USRCS Cutters conducted operations against these pirates, the depredations far outstripped the abilities of the USRCS and Congress ordered the construction and manning of six frigates on 27 March 1794;[11] three years later the first three were welcomed into service: the USS United States, USS Constellation and USS Constitution.

From this we can see that Congress formally authorized a national army on 14 June, 1775 and a national navy (if you consider 2 ships to qualify as such) on 13 October, 1775. Since these are the dates both branches of the military regard as "official", I stand by my assertion regarding the question of "senior service" within the US military hierarchy. I seem to recall from my own service that the Navy, at least, pretends not to notice such petty distinctions and the Army just assumes its "natural" superiority in the scheme of things. Until it needs a ride somewhere.

I don't really expect any of this to settle the question, of course, but it does make for slightly more substantial filler than available elsewhere. :)