The K-Boats were an attempt to build a fleet of "underwater cruisers"-- huge submarines that could travel on the surface and operate with surface vessels, rather than alone (as had been the norm) and then dive to attack, thus increasing protection of the surface vessels. The key was that they were equipped with steam powered surface turbines rather than standard diesel engines (but were equipped with electric motors for undersea use.) The "Ks" were the largest, most powerful submarines built until the advent of the nuclear boat fleets in the 1950s.
The vessels were plagued with disasters-- crewmembers were killed in virtually all of them. They had been posted to picket duties, with the result that the crews were bored with little to do; they were undertrained and the submarines incorporated technology that was completely unfamiliar.
This book traces the boats from their genesis to their end. They were originally planned to counter Germany's high speed, ocean-going submarines. After WWI, when the files of the German High Seas Fleet were investigated by the British, they found that Germany had no such submarines and had never planned any. The K Boats were developed to counter a threat which had never existed at all.
Readers with an interest in naval submarine history and the way in which politics determines naval decision making should read this book. In addition to text it contains a host of photographs of K Boats underway and a fold-out of a schematic of a K. An excellent read.