British Singapore took far less time to surrender than I took to finish this book.  At over 600 pages, much of it dumps of primary and secondary information, this felt like reading the appendices of a book that was missing, something that took me at a high level through the fall of Singapore before plunging into detail.  If ever I have missed forest for trees, it was reading The Pregnable Fortress.  At the risk of sounding overly negative, I think this would be a great second book to read about the fall, after getting sense of the overall narrative and context from another source.  

The focus of most World War II writing, at least that I've been exposed to, has been the war in Europe, both western and eastern fronts, and secondarily the American effort in the Pacific after Pearl Harbor.  Until living in Singapore I had no sense of the importance Singapore had as an eastern bastion of the British Empire, and was widely viewed as "impregnable" (as the Titanic was viewed as unsinkable).  Expected to hold for weeks or months, in theory until the Royal Navy's Mediterranean fleet could be dispatched for relief, Singapore fell to the Japanese in 6 days.  In Churchill's words it was "the worst disaster and largest capitulation in British history".  Britain's stature in the Far East was permanently crippled. 

What I learned: While General Percival, Singapore's military commander, has been historically blamed for the surrender, the loss of Singapore arose from a blend of indifference and incompetence in London, including years of neglect by Churchill himself (manifested for example in a lack of adequate air cover), mass desertions by Australian and Indian troops, and petty infighting among senior British officials in Singapore and Malaya.   The British underestimated the Japanese almost to the end, and paid a rough price (though not I think as great a price as the Chinese population).

Unfortunately the Japanese were pushed too far into the periphery in the book – the dire situation with their supply lines and ammunition were presented almost as afterthought.  They were on the verge of ending the their advance when Percival capitulated, but little detail is presented on their situation or leadership.

A dense read, but worth it for a pacific war buff.