Atlantic Nightmare is a frustratingly flawed history of the long Battle of the Atlantic during WW2. For over 2000 days, Nazi U-boats faced off against Allied convoy escorts, sinking 3500 ships at the cost of near total destructions. The Battle of the Atlantic was one of the few things that made Churchill nervous, and if it had gone the other way, Britain might have been starved of precious raw materials, the Soviet Union's lend-lease equipment would be at the bottom of the sea, and the Nazis might have won.
Freeman centers his narrative on U-boat commander Admiral Karl Donitz, which is a good choice, as Donitz drove the battle. From the start, the Nazi effort was hampered by the usual weaknesses of fascism. Hitler had told Admiral Raeder, his Naval leader, that war would come in 1947. When it started in 1939, the fleet was half-constructed. U-boats were a tertiary concern behind prestige projects like Bismarck class battleships and Admiral Hipper class heavy cruisers. There were only a few dozen U-boats. They rapidly racked up an impressive list of kills, but their numbers were too low to cripple British shipping.
At the same time, British escorts were sadly insufficient in numbers and quality. There simply were not enough destroyers and frigates to cover every ship, and U-boat attacks mounted a devastating toll through 1942.
Spring 1943 was the decisive moment of the war. Admiral Max Horton had taken over command of British convoy escorts. Horton finally had sufficient ships, along with new technologies like centimeter radar and long range patrol planes. But the real advance was in training and morale. Horton formed permanent hunter-killer groups of ships trained to work together, stopped promoting successful officers out of convoy escort, and directed his ships to seek out and destroy the enemy rather than protecting merchant ships. The months of battle ripped the heart of Donitz's U-boat fleet, and they had a peripheral role for the rest of the war.
In Freeman's view, the Allies triumphed because they adapted faster and more successfully. Convoy escort was a priority from Churchill on down. New technologies, like centimeter radar, hedgehog mortar depth charges, the Leigh light, and ULTRA codebreaking, in combination with doctrinal advances in tactics and operations research, meant that the Allies were able to develop a decisive advantage in attrition and win the battle. Conversely, while Donitz was a skilled fighting admiral, he had a parochial view that the goal was tonnage sunk, and relied on a handful of skilled aces. As these experts were killed in combat, the U boat fleet suffered a fatal decline in efficiency. U-boats were only prioritized too late, after showpiece surface raids, the Battle of Britain, and then all-encompassing maw of the Eastern Front. And while Allied interservice rivalries were a problem, with heavy bombers diverted to the strategic bomber offensive rather than coastal patrols, it was far better than the Luftwaffe, which refused to support the German Navy as a matter of Goering's pride.
Good history is hard, and Atlantic Nightmare assumes you already know a fair bit about weapons and tactics in the period. The best example of a clear description of how the battle worked is an aside on operations research, where studies revealed that convoy defense was a matter of density of destroyers on the perimeter. Since the number of ships in a convoy is a matter of area, this meant that paradoxically, bigger convoys were easier to defend. A 100 ship convoy required 66% of the escorts of two 50 ship convoys. At the same time, it skips over figures who deserve more recognition. Dontiz is famous (partially because he was Hitler's successor and finally ended the Nazi regime), but I'd never heard of Admiral Horton, or a Captain Frederic John Walker, who developed tactics of the Western Approaches command, and while they're mentioned these Allied commanders deserve more space and consideration. These flaws, in combination with enough typos to be bothersome, drop this book down to three stars.