Between the World Wars, Germany's neighbors built impressive permanent fortifications such as the Maginot Line in France and Eben Emael in Belgium. As Germany rearmed in the 1930's, its army sought to acquire siege artillery appropriate to the task of reducing these forts. The result was super-heavy siege guns of truly heroic calibers.
This concise Osprey New Vanguard series book covers the development and fielding of these super-heavy German guns and mortars including: 54 & 60cm Karl Gerat, 80cm Gustav (the titan of artillery), 35.5cm Haubitze M1, the still operational WW1 era Guns and the Skoda siege guns. Also interesting is the comments in this book about ammunition, assembly and transportation, especially with this huge guns. The book comes with excellent color illustrations and well selected B&W photographs, also a table comparing the guns max. range, production and other things.
Then the narrative covers their wartime use especially in 1939-42 and their decline after 1943. and a brief conclusion.
In the event, none of these large guns played any significant part in the war; but their story remains a fascinating one and it is hard to imagine it being better presented. Excellent book for the ones who love war industrial marvels.