The Oxford Companion to the Second World War.
Ed: ICB Dear & MRD Foot.

Big old thing that can be found for very little money and covers almost every aspect of the history of the war in well-written concise sections written by leading historians in whatever area is being explained.

Indispensable and as near to comprehensive as I've ever found without any windy padding.

Cheers,
Adam

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"Wars cannot be fought with dream stuff" - Sir Percy Hobart.