I got a nice little booklet in the mail today, a 1952 UK Government paper on "Condensation Trails From Aircraft". It contains some interesting discussion on the science of contrails and experiments that were carried out during WWII to try to advance that science. Contrails were a major concern in WWII, as they were huge visual indicators of a plane's position. The thing that caught my eye the most though was the photo above, of what looks like a persistent contrail. Judging by the relative difference in the two circuits of the trail, it seems to be formed by one plane, and has persisted for several minutes at least. It is dated November 13, 1937, 11:30 a.m, and is attributed to the R.A.F. (The Royal Air Force in the UK). While there are written accounts of persisting trails dating back to the 1920s, this seems to be the very earliest photo of a contrail, 79 years old. Does anyone know of an earlier photo of a contrail?