Case Blue (German: Fall Blau), later renamed Operation Braunschweig, was the German Armed Forces (Wehrmacht) name for its plan for the 1942 strategic summer offensive in southern Russia between 28 June and 24 November 1942.

A continuation of the previous year's Operation Barbarossa and intended to finally knock the Soviet Union out of the war, the operation involved a two-pronged attack against the rich oilfields of Baku as well as an advance in the direction of Stalingrad along the Volga River, to cover the flanks of the advance towards Baku. For this part of the operation, Army Group South (Heeresgruppe Süd) of the German Army (Wehrmacht Heer) was sub-divided into Army Groups A and B (Heeresgruppe A and B). Army Group A was tasked with crossing the Caucasus mountains to reach the Baku oil fields, while Army Group B protected its flanks along the Volga.

Initially, the German offensive saw spectacular gains with a rapid advance into the Caucasus capturing vast areas of land and several oil fields. However, the Red Army decisively defeated the Germans at Stalingrad, following Operations Uranus and Little Saturn. This defeat forced the Axis to retreat from the Caucasus in fear of becoming trapped. Only the city of Kursk and the Kuban region remained tentatively occupied by Axis troops.

Case may refer to:

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 450–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory (RYB) where blue was considered a primary colour, its complementary colour is considered to be orange (based on the Munsell colour wheel).

In Modern English, "blue" is one of the basic colour terms, and one of the seven spectral colours, intermediate between violet (purple) and cyan. It comprises a considerable number of identifiable subcategories that can be identified with descriptive terms like navy blue (a dark blue), cyan blue (or "blue-green", on the boundary to the green range), or sky blue (azure).

The word itself was loaned into Middle English from the Old French word bleu, blo "pale, pallid, discoloured; blue, blue-grey", itself from an Old Frankish *blao.