I-18 belonged to the Type C class, big ocean-going cruiser submarines that the Imperial Japanese Navy designed for one thing: reaching across vast distances and arriving with a heavy punch. She measured 109 meters from bow to stern and could run 14,000 nautical miles on the surface without refueling - far enough to cross from Japan to the coast of Africa and back. Built at the Sasebo Naval Arsenal and launched in July 1939, she was fitted to carry a Type A midget submarine piggyback on her afterdeck. These were the throats of the war machine, conceived to slip torpedoes into harbors no full-sized boat could enter.

In May 1942, British forces had just seized the harbor of Diego Suarez to deny it to the Axis. A floatplane catapulted from another submarine confirmed the prize: the battleship HMS Ramillies lay at anchor. On the night of 30 May, midgets from the submarines I-16 and I-20 crept into the harbor. One torpedo tore a thirty-foot hole in the Ramillies; another sank the tanker British Loyalty. I-18's midget never joined them - its engine had failed, and she could not launch. The two crewmen of one surviving midget beached their craft, struck inland on foot, and were killed three days later in a firefight with Royal Marines. They had hoped to be picked up near Cape Amber. No one came.

Robbed of her midget, I-18 turned to the merchant lanes of the Mozambique Channel, the long corridor of water between Africa and Madagascar where freighters ran cargo north and south. On 8 June she sank the Norwegian merchantman Wilford, then heaved her useless midget submarine overboard. Through that summer she stalked the Indian Ocean, sinking and damaging ships from Mozambique to the South African coast. Not every attack was clean. When she torpedoed the steamer Mundra - a vessel crowded with survivors plucked from earlier sinkings - 155 people lived through it, and the hunt for I-18 sent dozens of Allied aircraft into the sky. She slipped away every time.

There is a particular sadness in how I-18 spent her final weeks. A boat built to hunt battleships across oceans was reduced to a cargo runner. By the end of 1942, Japanese troops on Guadalcanal were starving, cut off by American control of the sea and sky, and submarines were among the few vessels that could still slip supplies through. Three times I-18 crept to Cape Esperance on the island's northwest tip and pushed drums and a container of food and ammunition overboard for soldiers ashore - fifteen tons, then twenty-five, then eighteen. It was dangerous, unglamorous work, and it spoke to how badly the tide of the war had turned against the men inside her hull.

On 11 February 1943 she surfaced to report an American task force in the Coral Sea, some 200 nautical miles south of San Cristobal. A scout floatplane from the light cruiser USS Helena spotted her first and dropped a smoke marker on the water to mark the spot. The destroyer USS Fletcher came in fast, gained sonar contact directly ahead, and laid down depth charges at 15:27. Twelve minutes later, a great bubble of oil and air boiled to the surface. A heavy explosion followed. Then cork, splintered wood, and wreckage rose into a spreading slick. That was the end of I-18 - all 102 men lost. The Japanese declared her missing that same day and struck her from the navy list weeks later.