The earliest and most important expeditions of Americans into the unknown country which the nation had just purchased were led by young officers of the regular army.
Jefferson Entitled to the Credit.
The first of these expeditions was planned by Jefferson himself and authorised by Congress.

Nominally its purpose was in part to find out the most advantageous places for the establishment of trading stations with the Indian tribes over which our government had acquired the titular suzerainty; but in reality it was purely a voyage of exploration, planned with intent to ascend the Missouri to its head, and thence to cross the continent to the Pacific.

The explorers were carefully instructed to report upon the geography, physical characteristics, and zoology of the region traversed, as well as upon its wild human denizens.

Jefferson was fond of science, and in appreciation of the desirability of non-remunerative scientific observation and investigation he stood honorably distinguished among the public men of the day.

To him justly belongs the credit of originating this first exploring expedition ever undertaken by the United States Government.
Lewis and Clark Chosen.
The two officers chosen to carry through the work belonged to families already honorably distinguished for service on the Western border.