A Water Slug Firing Its Shot
It should come as no surprise that a person who is forced to remain submerged for extended periods of time and is confined in a tin can for those lengths of time might come up with ridiculous yet amusing practical jokes. At least once a week, for the purpose of training, torpedoes are launched from submarines.
After inflating the torpedo tube, they release it into the water using a “shooting” motion. The action that is being described here is referred to as “shooting water slugs.” New sailors who aren’t familiar with this hilarious term are often given the assignment of going to the engine room to get a bucket of water slugs when they make a mistake.