In 1937 the group received its first enclosed cockpit, monoplane fighter with retractable landing gear, the Seversky P-35, replacing P-26s and PB-2As. The P-35 was obsolete from the beginning of its operational history and replacement by the Republic P-43 Lancer began in 1940. This fighter too was unsuitable for modern combat, and preparations for the possibility of U.S. participation in the Second World War introduced the 1st Pursuit Group to the new P-38 Lightning in July 1941, with the 27th Pursuit Squadron receiving the first operational aircraft in the Army Air Force's inventory.