When Hawaii’s expansive Mauna Loa volcano erupted in 1935, it sent serpents of red-hot liquid rock slithering toward the town of Hilo, then home to 16,000 residents. Normally, during eruptions, there’s not much anyone can do except get out of the way. But that year, scientists decided to try something a little different.

On December 27, a small squadron of Keystone B3 and B4 biplanes flew over the torrents of lava threatening Hilo and dropped 20 bombs onto it, totaling 3.6 tons of TNT.

For all that furious firepower, the bombing wasn’t meant to destroy Mauna Loa or even to stop its eruption—only to divert danger by collapsing the rocky channels and underground tunnels the lava was following toward Hilo. This