1939 marked the beginning of the second World War. Although the United States remained neutral in 1939, it began to rearm, which helped to end the Great Depression. Albert Einstein alerted President Franklin D. Roosevelt of Nazi atomic-bomb research. That led to the Manhattan Project and the creation of the first nuclear weapons.

In the arts, author John Steinbeck published "The Grapes of Wrath," and Hollywood released one of the first color films, "The Wizard of Oz." "Gone With the Wind" also debuted on the silver screen.

Despite a gradual shift from a consumer-based economy to a defensive one, advertisers still used marketing as a tool, despite the fear of excessive spending.

Here is a selection of advertisements featured in HPAC Engineering, then called Heating, Piping and Air Conditioning, in 1939.