He served as a purser in the United States Navy and received a Presidential commission to gather information on the Oregon Country.
[2] During his naval career in 1831, Slacum was the purser aboard the USS Potomac as that ship spent four years at sea circumnavigating the globe.
[5] In 1835 Lieutenant Slacum was selected by President Jackson to travel to Oregon Country to gather information on the affairs of the region.
[8] Slacum then spent time interviewing Hudson's Bay Company officials such as Dr. John McLoughlin and James Douglas at Fort Vancouver.
[9] Here Slacum helped to convince pioneer Ewing Young to give up his efforts to build a distillery and travel to California in order to purchase cattle that would then be driven overland back to Oregon.
In his report that was read in Congress on December 18, 1837, Slacum details the activities in the region and advocated that the United States extend jurisdiction over this area with a border of no further south than the 49th parallel.