The Spad XI was a 2-bay biplane with swept-back and positive stagger wings, but without dihedral. It was powered by a 220 hp Hispano-Suiza 8Bc engine. In many respects it appears to be a scaled-up of the Spad 7. Ailerons were on the upper wing only. A trap door was located in the floor behind the cockpit of the Observer/gunner. The pressurized fuel tank held 140 liters and there was a gravity tank in the upper wing. The oil tank held 15 liters. The pilot had a Vickers gun and the gunner a single Lewis gun. A bomb load of 70 kg could be carried. The Spad XI was considered by the STAé to be inadequate as a 2-seat fighter. It was therefore decided to purchase the Spad XI as an Army Cooperation machine to replace the A.R. 1 and Sopwith 1A2.

The AEF acquired 35 Spad XI's in 1918. They were assigned to the 1st and 90th Aero Squadrons. The 1st Aero Squadron received its first batch of machines in February 1918. The unit replaced its Spad XI's in June 1918. The 90th Aero Squadron had a few Spad XI's on strength but they were apparently replaced the Sopwith 1A2's by May 1918