Also known as HAU in Germany from the german company name Hamberg Amerikanische Uhrenfabrik.
When Erhard Junghans, founder of the Junghans factory, died in 1876, his widow's son in law, Paul Landenburger, who had acted as business manager for Junghans, left to start his own factory Named Landenburger and Lang.
In 1883 the name was changed to the "Hamburg Amerikanische Uhrenfabrik",
HAC became a very well known German clock company. Kochmann has numerous references.
The company used many different trademarks but the best known is the "crossed arrows" symbol.
They eventually merged with Junghans in 1930