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The U.S. Army and the Lewis & Clark Expedition
Part 3: Preparations

Before Congress approved funds for the expedition, Lewis had already begun his preparations. From Jefferson he learned how to use the sextant and other measuring instruments. Together they studied Alexander MacKenzie’s account of his 1793 Canadian expedition to the Pacific coast and the maps in Jefferson’s collection. The president even had a special map made for Lewis that detailed North America from the Pacific coast to the Mississippi River Valley, with emphasis on the Missouri River. While the president drafted his instructions for the expedition, the captain worked on his planning and logistical preparations. In the evenings they discussed their concepts of the operation.

Leaving Washington in March, Lewis traveled to the Army’s arsenal at Harpers Ferry (at that time in Virginia), where he obtained arms, ammunition, and other basic supplies while supervising the construction of an experimental iron boat frame he had designed. Next, Captain Lewis went to Lancaster and Philadelphia, Pennsylvania, where Jefferson had arranged for some of the nation’s leading scientific minds to instruct Lewis in botany and natural history, medicine and anatomy, geology and fossils, and navigation by the stars. While in Philadelphia, Lewis purchased additional supplies, including a new condensed food, “portable soup.” He also arranged for theWilliam Clark by Charles Willson Peale, ca. 1810 (Independence National Historical Park) Army to provide transportation for his nearly four tons of supplies and equipment from Philadelphia to Pittsburgh. Lewis then set off for Washington for a final coordination meeting with President Jefferson.

When Lewis returned to Washington in mid-June, he was nearly two months behind his original schedule. He had hoped to be in St. Louis by 1 August; but after three intensive months of preparation, Lewis realized that the successful accomplishment of his mission would require more men and another officer. Now the president handed the captain his formal instructions. Foremost among Jefferson’s expectations was an all-water route to the Pacific. Lewis was told to explore and map the rivers carefully, to learn all he could about trade routes and traders of the region, and to study every Indian tribe along the way. Jefferson ordered Lewis to treat the Indians with dignity and respect and to invite their chiefs to come to Washington for a visit. Lastly, Captain Lewis was to describe the geography of the region and to bring back samples of plant and animal life. As they discussed the expedition, Jefferson acknowledged that it would require more men and another leader.

With Jefferson’s consent, Lewis wrote to his friend and former comrade, William Clark, offering him the assignment as co-commander. Both Lewis and Clark had served in the Legion of the United States under General Anthony Wayne a decade earlier. Clark had been an infantry company commander but had resigned his lieutenancy in 1796 to attend the business affairs of his older brother, General George Rogers Clark. In addition to approving the choice of William Clark, Jefferson ordered the War Department to give Lewis unlimited purchasing power for the expedition. Moreover, the president authorized the captain to recruit noncommissioned officers and men from any of the western army posts. On 4 July 1803, news arrived of the Louisiana Purchase, which resolved any international problems affecting the expedition. The next day Lewis set off for Pittsburgh.

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