Vintage NBC? chime. These were used for several other callings and likely some NBC radio stations at the hourly breaks during the early 1940s.
A note about NBC's fourth chime: The 3 chime notes were struck during the what use to be NBCs "station identification" at the top of each hour. When the 4th chime was struck it was a signal to the program or station manager to delay or suspend regular programming for a special announcement afterwards. During WW-II, it was often a report on the war effort.
Here's links to some web sites devoted to "NBC Chimes":