[1][2][3] He began his military career in 1792, with a Virginia militia or ranger company stationed in Wheeling fighting against Indians.

On the return trip, Gass was given command of the majority of the party for a short period while Clark and Lewis led smaller detachments on separate explorations.

He remained in the army after the expedition returned, serving in the War of 1812, in which he lost an eye, and fighting in the battle of Lundy's Lane.

During the Civil War, Gass at the age of 91 years had to be removed from a recruiting station after he wanted to enlist to fight the rebels.

They settled in Wellsburg, West Virginia, where he died in his 99th year, the oldest surviving member of the expedition.