https://taskandpurpose.com/thelongmarch/civilian-control-military-washington/
Congressional control of the military was explicitly part of the creation of the U.S. Army. On June 15, 1775, the 2nd Continental Congress chose George Washington to command the new Army. The next day he accepted.
The day after that, June 17, the Congress drafted his commission. That document states, in part, his obligation “punctually to observe such orders and directions, from time to time, as you shall receive from this, or a future Congress of these United Colonies, or a committee of the Congress.”
In other words, formal, explicit civilian control of the military not only predates the Constitution, it predates by more than a year the Declaration of Independence, and began with the selection of the first soldier in the Army.