In the 1915 Indianapolis 500, Aitken drove relief for two drivers, Gil Anderson and Earl Cooper (who ultimately finished 3rd and 4th).

In the 1915 Indianapolis 500, Aitken drove relief for two drivers, Gil Anderson and Earl Cooper (who ultimately finished 3rd and 4th).

Aitken started a total of 41 races at the Indianapolis Motor Speedway, which is, again, the most of any driver in the track's history.

Outside of his participation at the Indianapolis Motor Speedway, Aitken is known to have started at least 33 AAA-sanctioned races, from 1907 to 1916, and to have driven relief in at least three others.

Aitken is credited as co-winner of the American Grand Prize, which was held at the Santa Monica Road Race Course on Nov 18, 1916.