Starting from WWII takes a jolt of imagination, but you ain't seen nothing yet! The next stop is an alternate universe of Earth. This one has familiar geography, but the flora and fauna are "twisted."
The newcomers to this new world, they soon must decide whether to get involved with one of two sentient races. One looks like a "lemur/cat" and one is a standing "lizzard".
The extensive WWII naval world of the first part of the book is beautifully described. We get details and inner concerns of many of the crew, practical period naval tactics, and exciting battles with the "Japs". I find it surprisingly engrossing - so much so that I felt the disorientation of being yanked from 1942 reality to "somewhere else." I'm no historian, and I've been exposed to many WWII era novels, but this section is every bit as good as good as any novel. (See author's notes.)
Wham. Now we are thrust into the alternate universe. While geography is "mostly" unchanged, the crew of the Walker slowly begins to discover subtle changes. Giant "ancient" sea creatures, sea piraña, etc., then a huge wooden sailing ship with the Lemurians on board. Later, Bali looks normal, but deserted. Then a shore party is attacked by aggressive upright lizards.
Now the reader becomes immersed in alternate universe explorations. To me, tis is the really fun part. The expedition captain must make many decisions with only sketchy facts available. Alliances are forged, the modern men are thrust into the problems of how to secure survival of the ship and it's company while responding to the enemy threats of the lizard race.
It's all fun, and the lengthy volume never lagged my interest. There are some stretches of the imagination (such as quickly refining raw crude to both diesel and aircraft fuel), but I found them easily acceptable.