U-boat stories and statistics seemingly never cease to inspire naval historians, and this is the latest. After 1943 and the forced German withdrawal from wolf pack activity in the central Atlantic, one might think their sea-going presence would have been reduced.  Not a bit of it!  Operational numbers of German submarines increased to nearly 200, although activity was mostly restricted to the shallow waters off the east coast of America and Canada, the North Sea and the English Channel.  In all these areas the ratio of allied ASW forces to U-boats remained in favour of the allies.

The author claims that the introduction of the snort mast was a game changer, but the narrative is unconvincing. The early masts, whether hinged or telescopic, had numerous teething problems, and his contention that “Even today the snort remains a prominent feature in nuclear-powered submarines” is overstating his case, to put it mildly.  The use of an emergency aid for diesel-electric propulsion and air purification, should the reactor fail (or even temporarily shut down) is very rare in US and British submarines.  I don’t have reliable statistics but in more than five years at sea in three SSNs, I cannot remember a single forced reactor shut-down requiring the snort mast to be used in anger, although it was always nice to know it was available.  Nuclear reactors were built to such high engineering standards that any kind of breakdown was a very rare event.

Back to the U-boats, there is no argument that a submarine snorting is harder to detect than one on the surface, but as allied surface ship and aircraft radars became more effective, an array of masts including snort induction and exhaust, periscope, ESM, HF/DF and communications, provided ASW forces with significant radar and visual targets to assist detections, even if it was quicker for the enemy to pull the masts down than dive a whole submarine.  There were also some catastrophic mast failures and some carbon monoxide poisoning in the early days of the snort technology development.

Perhaps the most important part of the book is a record of the detailed whereabouts of individual U-boat patrols in late 1943 up to the end of the war. Submarines only became lethal weapons of war when they acquired almost unlimited mobility, substantial numbers of weapons and near independence of the sea surface. The U-boat was never in that league.