Well, they were testing American torpedoes against the battleship hulls. Nope, no damage here!!! In fact, these hulls are so good the torpedo either veers away from it, runs underneath it, or just harmlessly thuds into the side without exploding! Damn, those new battleship hulls are good!
Good one! At least your joke wasn’t a dud!
In the article, they "simulated" a torpedo blast by putting dynamite on a raft next to the test design.
I'm sure it was because they didn't was a real torpedo, um, a "live" torpedo, fired in the area just for safety, not because the easily available ones were made for the US Navy...