- Earlier in day 15, Drona is killed by Dhrstadyumna. The Kaurava army literally comes unraveled until Ashwatthaman hears the news. The boy is outraged at the way his father was treated and swears revenge on both Dhrstadyumna (for killing him), and Yuddistira (for betraying his trust).
Drona's son then pulls the army together and rushes to battle waving his WMD. First he tries to use the Narayana weapon, but Krishna is too tricky for that-- he knows its weakness, which is that it is ineffective against unarmed men. The Pandavas all drop their weapons and the bomb is a dud. One other problem with the Narayana weapon: it's only good for one shot. So much for that.
Next, he pulls out his Agneya weapon, which is pretty much like a thermonuclear device. Without a second thought, he gets into range with Arjun and sets the thing off. It wipes out perhaps half of the Pandavas' remaining army, but Arjun & Krishna simply brush off the ashes and resume fighting. Not even nukes can take out the incarnated Rishis Nar & Narayan!
Ashwatthaman asks heaven why his nuke failed to have the desired effect, and Vyasa shows up to explain that while his power derives from Shiva, Krishna's power derives from Narayana, so there's no comparison.
Finally, we find a funny reference to Sanjay rushing back to Hastinapur to report on the war. What happened to his divine vision? My guess is that originally the author had him running back & forth from the battle to the palace to report to the king what had happened. This proved to be too limiting for the author's desires, so he switched the premise to include divine sight. But then he forgot to expunge the earlier device from the books he'd already written!