"Blockhouses generally measured 30 ft. along the front, with a width of 10 ft. They were sunk three feet into the ground and stood 7 feet above it. The front was up to 30 inches thick. Massively strong, a blockhouse was virtually impervious to shell-fire; even a heavy shell would merely knock a large chip off the edge."
Anyone who has seen the the pill boxes and bunkers built on the Hawaiian islands by American Engineers shortly after the Pearl Harbor attack would immediately know that they had never studied these Western Front structures -because it would be clear to them that these could never have withstood a naval bombardment.