1:35 German SD KFZ 135 Ambulance operation "BLAU" STALINGRAD 1942 from RPM

Case Blue (German: Blau) was the German Armed Forces name for its plan for the 1942 strategic summer offensive in southern Russia between 28 June and 24 November 1942.The operation was a continuation of the previous year's Operation Barbarossa, intended to knock the Soviet Union out of the war. It involved a two-pronged attack: one from the Axis right flank against the oil fields of Baku, known as Operation Edelweiss, and one from the left flank in the direction of Stalingrad along the Volga River, known as Operation Fischreiher.

The Lorraine 37L was a light tracked armoured vehicle developed by the Lorraine company during the Interwar period or Interbellum, before the Second World War, to an April 1936 French Army requirement for a fully armoured munition and fuel supply carrier to be used by tank units for front line resupply. A prototype was built in 1937 and production started in 1939. In this period, two armoured personnel carriers and a tank destroyer project were also based on its chassis. Mainly equipping the larger mechanised units of the French Infantry arm, the type was extensively employed during the Battle of France in 1940. After the defeat of France, clandestine manufacture was continued in Vichy France, culminating in a small AFV production after the liberation and bringing the total production to about 630 in 1945. Germany used captured vehicles in their original role of carrier and later, finding the suspension system to be particularly reliable, rebuilt many into tank destroyers (Panzerjaeger) of the Marder I type or into self-propelled artillery.

The Marder I "Marten" (Sd.Kfz. 135) was a German World War II tank destroyer, armed with a 75 mm PaK-40 anti-tank gun. Most Marder Is were built on the base of the Tracteur Blindé 37L (Lorraine), a French artillery tractor/armoured personnel carrier of which the Germans had acquired more than three hundred after the Fall of France in 1940.