Today, if an operator encounters a text that is garbled, she or he will say, among other things, that it is “hammered.”  

During the American Civil War, an operator would describe the same sort of text as “bulled.” The derivation is unclear, but Eric Partridge’s Dictionary of Slang and Unconventional English defines “bull” as meaning a ludicrous jest or seif-contradictory statement, an inconsistency unnoticed by its perpetrator and often producing an unintentional pun.

Source: NSA