According to the North American train whistle code, one long whistle then three short whistles means only one thing: it’s time to jump off the train and attach the torpedoes.
First of all, I only just discovered that there’s such a thing as a train whistle code. Think of it like Morse code. Two long whistles: the train is heading off. Three short whistles: the train is backing up (or, if it’s already moving, the train is stopping at the next station.) Lots of short whistles: there’s something on the tracks, look out look out.
But then there’s this one signal. One long and three short whistles, which means “Instruction for flagman to protect rear of train.” I imagine this as a Wild West shootout kind of situation, but it’s actually an interesting instruction.
Imagine this: you’re on a train in the middle of the night and it breaks down. You’re stuck on the tracks, and none of the trains behind you know about it. What can you do? The whistle code instructs the brakeman at the end of the train to jump out and run off down the tracks as fast as they can. When they’ve run two miles, they light some flares and deploy some torpedoes as a warning for any other trains approaching.
You can tell I went down the Wikipedia rabbit hole on this one; what the hell is a torpedo? Quite simply: they’re tiny explosives that you strap to the train tracks. If a train drives over them they explode, making a big noise but not doing any damage. The train driver – sitting, as they do, near a very noisy engine – hears the bangs and knows to slow down the train… thus protecting the stopped train ahead from a calamitous collision.
The whistle code is pretty much defunct these days, as are torpedoes because trains are soundproofed.