While the KPD ran in elections they were also building their militia, the Rot Front.

Mike Ely of Kasama Project has an article giving an overview of Communist electoral tactics here.  It makes it quite clear that the question of how Communists approach elections is important, but that the options are not either armed revolution or parliamentary cretinism.  Context is critical.

From “Communist Electoral Tactics Part 2: Re-invented According to Conditions“:

However on the question of participation in elections, it is worthwhile to consider this:  The KPD had attempted at least two armed insurrections in Germany (the somewhat half-baked uprisings of 1919 and 1923), and they were very closely associated with a very nearby existing socialist state (the USSR). So no one was confused about what they stood for — no matter what they said, a vote for the KPD was a vote for socialism and armed revolution.

(Just like a vote for Panther leader Eldridge Cleaver in 1968 was a delightful way to say fuck you to the whole american system — because everyone knew that the militant  Black Panther Party was sweeping armed negation personified.)

The opposite is true of socialists running in the U.S.: here no matter what you say (“revolution, blah, blah, blah…”) the fact that you are running for the fucking senate or city council, symbolically implies (under current conditions) an implied legitimization of all that… the system, its offices, the constitution, “American democracy,” the will of the people etc.

Kasama Project has more articles on elections here, here and here.