Some WW2 humor here in the depiction of the Martian encampment. Grape shot is a kind of artillery ammunition.
At the time of this short, the concept of humans living on the moon, or Mars, was quite popular. Numerous films and TV series would explore the idea over the coming decades.
Popeye yells Heaven Can Wait!, a reference to the 1943 film of the same name.
This is the first animated cartoon to depict alien invaders.