It is true the Constitution does not specifically prohibit standing armies, but the Framers view of them was clear. It is one of the reasons the US sought independence from England.
Article 1, Section 8 provides Congress with the power to "To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years."
The two year appropriation was certainly a way to provide federal funding for the training of an army in times or war, but was to prevent standing armies in times of peace. But of course, Congress will just appropriate money every two years if need be. I seriously doubt the Framers intended it to be that way though, as many of them were publicly outspoken against standing armies.
"...but if circumstances should at any time oblige the government to form an army of any magnitude, that army can never be formidable to the liberties of the people, while there is a large body of citizens, little if at all inferior to them in discipline and use of arms, who stand ready to defend their rights..." -Alexander Hamilton
"What, Sir, is the use of a militia? It is to prevent the establishment of a standing army, the bane of liberty.... Whenever Governments mean to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise an army upon their ruins." -Rep. Elbridge Gerry of Massachusetts
The truth is that the Constitution provides a way to fund organizing, training, and arming a force indefinately, but it is not the army. It is the militia.
Part 13 of Article 2, Section 8 empowers Congress "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."
So here is the force that the Framers intended to regularly provide funds to train and arm. The People. So where’s my M16? [:D]
SOL