I am puzzled why there are only 141 documents. There should be thousands. The US Army has been around a long time and bureaucracy begets documentation.
This is only a subset, apparently only those TM's in the 5 series. Explore the Publications dropdown to find thousands more Technical Manuals and other publications.
These appear to all be from the Corps of Engineers. The menu pulldown shows entries like "TM - Technical Manuals (Range 1-8)" that have thousands of entries each. One example: https://armypubs.army.mil/ProductMaps/PubForm/TM_1_8.aspx