Like (I suspect) many British readers, I came to this book remarkably ignorant of what went on in the Baltic during WW2. My own Cold War sea trips to Kiel, Aabenraa, Korsor, Copenhagen. Gdynia, Stockholm, Helsinki and Leningrad were all within the frame of their time; they had no recent historical dimension. I emerge much better informed after this encounter with Groos who has pulled together, via forty years of research, a remarkably coherent narrative, comprehensive although necessarily economical, from records in at least twelve different national languages, covering not only purely naval events but the political and strategic background for the nine littoral countries, Norway and Britain. The level of detail crammed in is extraordinary. As to the naval, his own background as a naval officer (turned history lecturer, and alumnus of the RN Staff College at Greenwich) ensures an absence of solecisms relating to maritime matters. He has also mastered an environment where in effect two different wars were going on, with ice in winter, and without in summer.
The struggle in the Baltic exhibited key turning points such as the occupation of Denmark and Norway in 1940 (triggered, the author states, by the Altmark incident showing how events far away in the South Atlantic could affect decision making in the North), Barbarossa in 1941, the military recovery of the Soviets in 1942, and the Normandy Invasion of 1944. The book is arranged in roughly equivalent chronological sections, within which each country situation is dealt with separately. Within each of these sub-chapters we see for instance the equivocal situation of Finland with scores to settle and territory to recover from the Soviets, and (with hindsight) how a more vigorous opposition to the invasion of Denmark might have unpicked that of Norway. The recruitment of Dutchmen, Danes, Norwegians and Estonians into SS units is set against the sabotage and other tasks bravely carried out by the Danish Resistance. Those who had backed Hitler had to apply a fairly heavy new coat of makeup as the tide turned, particularly the Swedes whose interpretation of neutrality left something to be desired from the democracies' point of view, although the desire to avoid a direct invasion - those 380,000 German troops retained in Norway were a significant threat although they were also insurance for U-boat basing as Germany lost her French Atlantic ports - needs to be borne in mind. Sweden does not come out of this narrative with clean hands, to put it mildly. The cross-connections between the Baltic and other theatres are well covered, particularly how the German surface fleet was pretty much annihilated outside the Baltic lake and therefore irrelevant within it until it found a role during the German collapse. The 'lake' of course is nearly a thousand miles long and, from a naval point of view, busy indeed, with the Germans seeking to control both its entrance and those of the gulfs of Finland and Bothnia. The interplay with other theatres includes the destruction of Tirpitz by RAF Tallboys, thought by some British commentators to be not entirely necessary, removed a German asset wanted in the Baltic for naval gunfire support, a process the Germans learned rapidly following being on the receiving end in Normandy. The same Tallboys also took out Scheer, Lutzow, Hipper and Emden thus relieving pressure on the Soviets. RAF and USAAF bombing also targeted the building and deployment of advanced Nazi submarines.
Technically we see a strong emphasis on submarine and mine warfare, including extensive aerial mining by the RAF, and note the Germans sometimes hoist by their own petard with critical losses in their own minefields, in spite of devoting huge resources to minesweeping, the same frustrated at the end by want of air cover. The sheer size of the armies (and casualty numbers) on the Eastern Front is a key background feature; so also the steady erosion of the initial German air advantage. At the end we see Doenitz' (his character as an enthusiastic Nazi fully delineated) remarkably successful seaborne recovery of thousands of refugees, in spite of interdiction by Soviet submarines and aircraft, as it dawned on the Germans that it was well-earned payback time for the panoply of abominations perpetrated by the Germans in Eastern Europe when they were winning; German mass murder and other atrocities continued right up to the end.
A week before the end the British Army appear, taking Wismar and ensuring the eventual freedom of Denmark and that the Kiel Canal remained available to the West.
To accommodate a more general readership, there are blockouts throughout the book explaining technical matters. The volume is generously larded with illustrations, positioned appropriately throughout so as to support the narrative.
This book has been a remarkable contribution to my education and I fully endorse it to a general, as well as a professional, readership. There are quite a lot of surprises. I have also hugely enjoyed it, if that is the right verb to use regarding reading about a colossal human catastrophe.