"Springtime for Hitler" is the fake musical at the heart of Mel Brook's movie and later musical "The Producers." It is supposed to be a play that is so poorly written and in such poor taste that it is sure to be a flop. Thus allowing the producers of the title to profit from over-selling shares in the production to investors. However, the audience takes the musical to be a joke and it turns into a big hit, dooming the producers.
"Springtime for Hitler" is also the song that opens the fake musical. It's lyrics famously include the lines, "And now it's.../Springtime for Hitler and Germany/Deutschland is happy and gay!/We're marching to a faster pace/Look out, here comes the master race!"