[2][3] Helm was commissioned a captain and asked to raise and lead a company of Virginians by the newly promoted Lieutenant Colonel George Rogers Clark.
Leonard Helm, who had served with Clark during Dunmore's War and had spent a lot of time in Kentucky, was given command of one of the initial four companies created to form this regiment.
[6] Knowing that the British did not fully understand his tactical situation, he demanded and received favorable terms of surrender.
When Colonel Clark heard about the surrender several weeks later, he and his force made a bold march through icy winter weather and laid siege to Fort Sackville.
On 5 March 1779, Helm led a small force of 3 boats and 50 men up the Wabash River from Vincennes and captured a fleet of 7 boats, 40 prisoners (among whom, Clark noted in a letter to George Mason, was 'Dejeane, Grand Judge of Detroit'), supplies, and trade goods that were sent to reinforce Hamilton at Fort Sackville.
This was a valuable (prize) seven boats loaded with provisions and goods to a considerable amount.When Clark left Vincennes for Kaskaskia on 20 March 1779, he again appointed Captain Helm as commandant of the town, as well as Superintendent of Indian Affairs.
A small band of Delaware from a village called Lechauwitank, between the forks of the White River, ambushed the traders, killed them, and plundered their goods.
The entire village was destroyed, the surviving men were tomahawked to death in Vincennes, and the women and children were sold into slavery.