Subsea Crawlers were autonomous underwater vehicles that crawled on the sea floor. During the mid-21st century, some subsea crawlers became manned.
(Note: The background section of this page uses most of the same words as Terra Futura's page on underwater gliders to save time.)
The first autonomous underwater vehicle, or AUV, was developed in 1957 at the University of Washington. It was known as the Special Purpose Underwater Research Vehicle, or SPURV. This helped scientists learn more about ocean physics. Its successor, SPURV II, was launched in 1973 for the same purpose. At the same time, scientists from MIT were developing their own AUVs. So was the Soviet Union. Later AUVs had a wider range of applications. However, they could only operate for hours without a tether to a surface ship. The underwater glider changed that.
Underwater gliders could keep working for weeks or even months. The design dated back to the 1980s with Henry Stommel who was collaborated with DARPA at the time. A prototype was constructed in 2003 by Webb Research. In 2009, Rutgers built an underwater glider that took 221 days to cross the Atlantic. Underwater gliders flowed with the current, but used wings and buoyancy changes to maneuver. They also took advantage of thermal stratification. When the glider was near the surface, the wax in the engines expanded. In deeper water levels, the wax compressed. Both wings had antennae, so that when the underwater glider was at the surface one of the wings would go out of the water to receive GPS signals for navigation. In the early 21st century, the deepest an underwater glider ever went was 1,500 meters. Later models would go 3,300 meters. Batteries controlled the pitch and orientation and powered the sensors and radio. Underwater gliders provided valuable data on Earth's oceans. Later on, they would be used for oceans on other planets and moons. The technology was also used for the subsea crawler.
Tech Level: 10-11
Subsea crawlers could be used for many jobs. They could be used in cable laying and maintenance, excavation, exploration, search and rescue, aquaculture, surveying, mine laying and removing, mining, maintenance, salvaging, construction, hauling, and weapons. Search and rescue was the most notable application. In South Korea, scientist built a six-legged crawler that sped up search and rescue after the Cheonan sinking incident. This was the first subsea crawler with legs. Control was done by communication cables in the early 21st century. Later versions were more autonomous and some were even manned. Manned crawlers had a variable buoyancy system to float. They were also modular to make them cheaper. Some had open-pressure systems. Others had closed pressure systems allowing them to operate at extreme depths. There was the risk of explosive decompression in this case, so safety features were added in. Overtime, subsea crawlers gave way to mobile underwater habitats.