The Spads in the photo. On 29th May 1917, 40 Sqdn were based at Bruay and stayed there until 4th June 1918. In February 1917, 23 Sqdn were re-equipped with Spad VIIs and on 29th May 1917 moved to - guess where - Bruay, staying till 13th June 1917. Interesting?. Unless you have other clues in the material, I would say that the Spads in the photo are of 23 Sqdn. Bruay is slightly south- east of Béthune.