FAT MEN NOT WANTED
Oddly enough, small, slender men were preferred for submarine duty, not because of lack of space, but because it was apt to be very cold in a submarine, particularly in the winter-time. The water cooled off the boat when the submarine was traveling submerged, and the motors gave off little heat; while when the vessel was running on the surface the rush of wind to supply the engines kept the thermometer low. This meant that the men had to pile on much clothing to keep warm, which made them very bulky. The hatchway was none too large and a fat man, were he bundled up with enough clothing to keep him warm, would have a hard time squeezing through.
In the center of the vessel was the main hatchway, leading up to the conning-tower, which was large enough to hold from three to five men. This was the navigating-room when the vessel was running submerged, and above it was the navigating-bridge, used when the submarine was on the surface. In the conning-tower there was a gyroscopic compass; a magnetic compass would not work at all inside the steel hull of the U-boat. And here were the periscopes or eyes of the submarine, rising from fifteen to twenty feet above the roof of the conning-tower. There were usually two periscopes. They could be turned around to give the man at the wheel a view in any direction and they were used sometimes even when the vessel was running on the surface, to give a longer range of vision.