Bored as usual, Homer decides to take up a new career in the Navy, where he single-handedly cuts the ribbon on treason season by charting a submarine into Russian waters. Meanwhile, Bart gets his ear pierced. Guest starring Bob Denver, Rod Steiger as Captain Tenille, and Michael Carrington.
Homer, Lenny and Carl all want a doughnut, but only one is left. Homer thinks up a solution: he places the donut in the reactor core in an attempt to make it huge. Within ten minutes, the power plant is on fire and Homer is fired (after initially pretending it is his first day). While lying on the couch at home, Homer sees a recruitment ad on TV for the Naval Reserve and decides to make a difference and enlist. Moe, Barney, and Apu also decide to join him. Meanwhile, the whole school is impressed when Milhouse gets an earring. As earrings become a fad, Bart gets his ear pierced, much to Homer's outrage. However, as Bart attempts to impress everyone in school with his earring, only to find out that every student has his/her own earring, except for Lisa, who is forbidden by Homer to do so.
Homer and the others attend the Naval academy and soon graduate. They are later forced to participate in the annual war games and are placed on board a Nuclear submarine which is under the command of Captain Tenille. Homer says goodbye to his family, except for Bart due to the earring. Bart bitterly gives the earring to Homer, who then boards the submarine. Captain Tenille takes a shine to Homer and when the Captain goes to check on a problem in the torpedo hatch, Homer is left in charge. At this point, an enemy submarine approaches Homer's, and Homer immediately responds by giving the order to fire a torpedo. However, Captain Tenille is in the torpedo hatch and is fired at the other submarine. The other sub fires back at them, and Homer gives the order to retreat. The submarine ends up in Russian waters and is interpreted by the United States government as an attempt to defect. This event creates a political schism between the USA and Russia; the Russian government reveals that the Soviet Union still exists, and that its fall was merely a ruse. Nuclear war is anticipated until the US Navy drops depth charges on Homer's sub, aiming either to destroy it or force it to surface. The consequent explosion causes a pinhole leak in the submarine's wall. The crew all believe their situation is fatal until Homer remembers the earring he took from Bart. He uses it to plug the leak and saves the submarine.
The vessel surfaces and Homer is taken to be prosecuted; however, he is let off the hook because all of the officers at his hearing are under indictment for various offenses. Homer receives a dishonorable discharge and forgives Bart, as the earring saved his life.
"Simpson Tide" was one of two season nine episodes that was executive produced by Al Jean and Mike Reiss, who together were the showrunners for the third and fourth seasons. Although Jean would later return to run the show, it was the last episode that Reiss received an executive producer credit for. Joshua Sternin and Jeffrey Ventimilia, the episode writers, were working on Jean and Reiss's show The Critic at the time, and pitched an episode where Homer joins the naval reserve. Although the episode is partly based on the film Crimson Tide, the original episode pitch was made before the film was released. After the release of the film, the writers decided to start incorporating stuff from the movie in the script. In the original draft, Bart snuck on board the submarine with Homer. They were trying to do it "for the comedy of it", but couldn't get the draft to work, so it was cut. It was difficult for them to figure out how to get the captain off of the sub and they eventually decided to have him shot out of the torpedo tube.
Michael Schiffer, one of the writers of the film Crimson Tide is said to have enjoyed this episode. Mike Reiss considers the sequence where Russia returns to being the Soviet Union to be "the nuttiest the show has ever been".