At last! I was able to get hold of an AAC Sales Catalog, and low and behold there it was, the same gun that appears in the Swiss book on fortifications, labeled as an American antitank gun! In the AAC catalog it is a 37mm Infantry/Mountain gun also touted as being useful as an antitank gun too. The only difference between the catalog picture and the one in the Swiss book is the carriage. Here is the gun as it appears in the AAC sales catalog.