'Chattanooga Choo-Choo' was an Allied air offensive by fighter-bombers of Air Chief Marshal Sir Trafford Leigh-Mallory’s Allied Expeditionary Air Forces (Air Marshal Sir Arthur Coningham’s British 2nd Tactical Air Force and Lieutenant General Lewis H. Brereton’s US 9th AAF), supported by the fighters of Lieutenant General James H. Doolittle’s 8th AAF, against German railway targets (locomotives and rolling stock) in North-West Europe (20/28 May 1944).
The object of the offensive was to reduce the quantities of such equipment available to the Germans as a means of reinforcing their armies in North-West France once 'Overlord' had been launched.
The German plan for defence against an Allied invasion called for any such landing to be checked on the beach before the Allies could establish a permanent beach-head capable of rapid expansion into a sizeable lodgement. This required rapid response by strong mobile German forces, as soon as the first Allied troops had landed and their precise location had been established. To prevent such a response, the Allies developed the Transportation Plan, designed to destroy and disrupt German transportation and communications immediately before the invasion.
In 'Chattanooga Choo-Choo', the British 2nd Tactical Air Force and US 9th AAF, supported by the fighters of the 8th AAF, targeted railway facilities, marshalling yards, bridges and rolling stock in the western part of occupied France in the weeks before the D-Day launch of 'Overlord'. Hundreds of locomotives and trains were strafed and destroyed by fighter-bombers, while attack aircraft and medium bombers struck at railway marshalling yards and vital bridges.
It is also worth noting that to supplement the basic elements of the Transportation Plan, Leigh-Mallory authorised wide-scale fighter sweeps against moving trains on 20 May, when civilian passenger traffic was believed to have ended. For some time fighters had been attacking trains, to the nervousness of commanders who feared the political repercussions to the possibly indiscriminate killing of civilians. Now the practice was carried out openly and on a large scale, and in the following two weeks fighter-bombers destroyed or damaged about 475 locomotives and cut the French railway lines at 150 different points. The most sensational attacks were those of the 'Chattanooga Choo-Choo' effort, which began on 21 May, when 763 of the Allied Expeditionary Air Forces' fighter-bombers swept over the northern half of France and 500 8th AAF fighter-bombers ranged over Germany firing at and bombing trains. Another episode was that of 25 May when three fighter groups of the 9th AAF operated over the Rhineland and northern France and more than 600 8th AAF fighter-bombers shot up trains in Belgium
Other major 'Chattanooga Choo-Choo' missions were carried out by 571 8th AAF fighters in eastern Germany and Poland on 29 May and by the 9th AAF in France on 2, 3, and 4 June. These operations furnished good practice for fighter pilots in attacking ground targets, a skill they were to develop to a high degree after the invasion, and they brought about enormous disruption to German traffic and destruction of equipment while producing important psychological effects on railway personnel.
French train crews deserted in large numbers, especially after fighters began to drop belly tanks on stalled trains and then ignited the spilled residual fuel and fuel/air vapour by strafing. This situation caused the Germans to employ crews of their own nationality on the more hazardous runs, and after 26 May
railway operations in daylight were sharply reduced even in cases where the railway lines were still unbroken.
The German high command believed the deceptions of 'Bodyguard' and similar deception and cover undertakings, and therefore kept many of its best units awaiting the 'real' invasion in the Pas de Calais region for some two weeks after D-Day. German commanders trying to rally forces to Normandy were completely frustrated to find their telephone and telegraph communications cut, road and rail bridges destroyed, and railway and canal transport in chaos as a direct consequence of the success of 'Chattanooga Choo-Choo' and the French resistance forces.