From Article I
To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;
It says nothing about how long the army can exist, but you cannot fund it for more than two years without congress re-approving it.
You leave out several clauses.
To provide and maintain a Navy;
To make Rules for the Government and Regulation of the land and naval Forces;
To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
First there is no such restriction on the navy.
Second, the army was meant to be drawn out of the state's militias.
Which means that the navy was meant to be permanent..the army was meant to be "as needed". And the fact that it was drawn out of state militias indicates that it was meant to be citizen based and de-centralized.
