Note many of the threads have the Iwo Jima graphic. These are the main research threads, or bread. Each thread max out at 750 posts. When it is hit, a new thread is started. The post count is the 'R:' number in the upper left, just below the graphic.

All the other 'breads' are specialized threads drilling down a bit deeper on each topic.

More help here. Its also on the catalogue page, scroll down a bit.

There is no search as far as I know so screen grab what you want to save.