My first experience reading Erik Larson was DEVIL IN THE WHITE CITY, which was about the Chicago World's Fair in the late nineteenth century. Coincidentally a serial killer was stalking the denizens of the “Hog butcher of the world” at the same time.
As you can tell from the bibliography of DEAD WAKE, Larson is a first rate researcher, never accepting established fact (such as Churchill's claim that two torpedos struck the Lusitania).
The big mystery as I see it, and as Larson hints at, is why the Lusitania never got an escort when the Germans had warned Americans not to travel on the ship in the New York Times. The British also had information that there were submarines in the area; the Russians had stumbled over the German's wireless code book and had given it to Room 40, the British intelligence serve, led by Winston Churchill the First Lord of the Admiralty. They had also been tracking Unterseeboot-20, the sub that sank the great liner, led by Walther Schwieger, since it left port. One begins to wonder if the British were hoping the Lusitania would be sunk, thus bringing America into the war. There was also the rumor that the Lusitania was carrying badly needed munitions. The Germans certainly thought so as three German stowaways were captured prior to leaving New York.
Larson presents Churchill as a conniving sort of man throughout the book. For instance, he blames the captain, William Thomas Turner for not using a zigzagging pattern and staying in mid channel as directed by Room 40. The messages Turner received were ambiguous to say the least. If he had maintained his original course, Schwieger, who had given up and was on his way home when he stumbled across the Lusitania, never would have a chance at the ship.
We also see President Woodrow Wilson, depressed after losing his wife, but determined to keep the United States out of the war. But he has a new love, Edith Galt, whom he's determined to woo. She's reluctant since it had only been a year since Wilson lost his wife.
Ironically, the most interesting character in the book is Turner, not your typical Cunard captain, who refers to the passengers as “bloody monkeys.” He would rather eat in his room than preside over the captain's table during dinner. It looked like Turner had planned to go down with the ship, as Captain Smith of the Titanic had, but his life jacket saved him and he went on to captain other Cunard liners and was sunk a second time, surving that one too. Turner started as a cabin boy and worked his way up to captain; as a result the reader has a great deal of sympathy for the man.
Larson ferrets out other passenger stories, perhaps the most interesting is that of the spiritualist, Theodate Pope, whose body was found, apparently lifeless, until Belle Nash, a fellow passenger, noticed signs of life, as she was laid out among the dead. Pope returned the favor by putting Mrs. Nash in her will.
It's these little stories that make DEAD WAKE an enjoyable read. Upon reading the German warning in the TIMES, passenger Dwight Harris had his own life jacket made. Seems like he knew what he was doing as many passengers died because they had their life jackets on wrong and entered the water head first.