A railroad torpedo in use

Prior to working on the track, work crews strapped torpedoes like this to the rail using the soft, lead straps. This device was strapped to the rail about 0.25 to 0.5 miles (0.40 to 0.80 km) from the work site. They would be placed in a pattern so that when an oncoming train ran over the torpedoes, the train crew would hear a bam...then bam, bam, or some pattern like that to alert them to the work crew ahead. The bang was so loud that the work crew could hear it too, alerting them to a train approaching. Once the track work was done for the day, the track crew removed the torpedoes prior to leaving the work site.

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