The Phantom City

I can only read one or two of these a year. I like the adventure and the outrageous plots
but the misogyny and racism, while not excessive, are annoying.
Women are instantly and desperately attracted to Doc and generally are decorative to the plots.
And any culture that isn't white America is described as lessor.

The writing style is irritating as well.
In this book, rain is described as , “drooling”, “leaking”, and “sobbing”.
Doc likes to ride on the outside of cars and is said to not get wet when it rains.
He also can't get sunburned either.
He (and one or more of his team) are familiar and often fluent in all human languages.

He uses sonar and underwater breathing gear. I later found out that at the time these were written, a form of sonar did exist.
And people had been using underwater breathing gear at least as far back as Jules Verne, so its use here is not surprising.

But the bad guys have a weapon that is clearly a magnetic rail gun and I haven't heard of that tech either existing or used in previous SF&F works.

So, if you like this sort of thing, then this is the sort of thing you will like (Thanks, Don Thompson).