Admiral Byrd Diary
The story of the German expedition to the inner earth actually begins in Tibet in 1925 when a Russian expedition discovered information about an ancient civilization and anti-gravity technology from some Tibetan Monks.
For those who study history, you will know about the how the nazi's searched the world for mystical items and symbols.
One of the area's of most intrigue to the nazi's was Nepal and the legend of Mount Meru and legend of a massive treasure in Gold being stored under one of the holy mountains, later identified as Mount Kailash.
As well as gold, there were stories of alien technology and of a companion location which was under the South Pole.
So the nazi's invested heavily in sending ships and submarines to the South Pole to survey both the land and sonar survey the underwater coastline for "openings" into this inhospitable region.
From many of the reports which were "floating" around after the second world war, it appeared that the nazi's had indeed found and made contact with some kind of civilization at the South Pole.
I will leave it up to you to do your own homework regarding verifying the above information.
The underwater entrance(s) spoken about in the nazi documentation may very well be the reason that the US Military sent their own submarine to sonar detect the underwater coastline.
Below are some images from the German Archives regarding these adventures.
For those interested in the strange annexation of the South Pole by the nazi's and the convoys of people they "supposedly" sent there, please research the following. New Swabia and NeuSchwabenland
Note that NONE of these people have ever been heard of since which leads me to think that they are either enslaved or eaten.