I picked this tool up last week at a thrift store. Someone must have been cleaning up grandpa's garage.
As you pull the handle when the wrench is in the position in the top photo, the jaw opens. You then flip the wrench over and as you pull it, the jaw closes. It has a very positive action.
Hans Dorn of Berlin, Germany applied for a U.S. patent for this tool in 1927, and it was awarded in 1931.
Interesting that the wrench is stamped "Foreign" on the handle.
Clever design, but ultimately destined for the dustbin of tool history, otherwise known as my workbench