The film's trailer
The race is on!
To determine who's faster at delivering the mail, a race is held against the bush plane. The first person to return to Nome with the mail is the winner!
When an air pilot named Duke states that air mail is the way of the future, Dispsy and Mel spread the word by starting a "barking chain" to warn the other dogs.
Note: This clip can only be played on YouTube. It's also in German.