Summary: What if the fastest method of world travel involved supercavitating submarines?
I remember the first time I went beneath the waves, despite my parents' assurances that I would come back up. I was a child at the time, and my father tried to reassure me as we boarded the ferry that took us to the sub-port. We descended on the passenger elevator, and I saw the craft beneath me: a spear-nosed submarine with nozzles around the fore. He told me it was a Sarissa-class vessel, named for a spear used in ancient times. It was named for a prototype warship that laid the foundation for modern global travel.
In earlier decades, my father explained international travelers flew across the skies in jet planes, and many still did. However, advances in materials and maritime engineering changed things. The world's oceans, once polluted with microplastics and increasing acidification, were harvested in an unexpected way. Cheap, scalable, and carbon-negative fuels were made from the substances polluting the seas. Former oil rigs and coastal stations were easily converted to produce energy-dense hydrocarbons, often as a stopgap for the limited rare-earth batteries of the day. These energy installations ushered in a new era of nautical travel.
Supercavitation, as my father explained, was how the Sarissa achieved supersonic speeds, which rivaled even the old Concorde passenger plane. The vessel released a pocket of gas, which then surrounded the whole vessel. Rocket engines activated within the gas pocket, allowing the craft to reach supersonic speeds. That was how we would cross the Pacific in a couple hours, as opposed to half a day.
We sat down on seats, and we buckled in. Father explained it was similar to a rocket launch, when astronauts went into orbit. I had on a projective child's seat, but he explained over safety measures. The entire cabin was reinforced with shear-thickening fluid, which tightened when pressure was placed upon it. Slowly, we descended to cruising depth. I felt the force on my chest, and I loved it. It was like a roller coaster on steroids. From then on, I saw why my parents loved to travel this way.
That's why I became a sub-wright.