The pilots of the 103d flew a wide variety of observation aircraft for the next 18 years. The most well-known of these aircraft was the JN-4 Jenny. The Jenny was an open-cockpit bi-plane; but was replaced in the 1930s and early 1940s with metal-skinned, prop-driven observation monoplanes. The list is long but shows the steady improvement in aircraft: PT-1, BT-1, O-1, O-2H, O-11, O-38, O-46,-47A, O-47B, O-49, O-52, O-57 and P434-1. The squadron also flew liaison type aircraft such as the L-4 and L-1B. The 103d Observation Squadron was ordered into active service on 125 November 1940 as part of the buildup of the Army Air Corps prior to the United States entry into World War II.