The unlocated naga field army that Carl's feints were designed to draw out — before it turned out to be gone.
Two of the four groups in Operation: Snake Pit existed largely to solve one problem: nobody knew where the naga army was. Tran's southern feint toward The Naga Castle and then west to Shanty Town was meant to force the missing army to appear and give chase, while Boomer and the 106th Bloody Leeches waited in reserve in case it instead punched through the thinned southern border.
All of that planning predated the news that Prepotente had gone ham on the naga forces, which reduced the missing army to a non-issue. Carl kept the plan anyway, because it was never really about the army.
The unlocated enemy force whose absence changed the meaning of Carl's diversions.