The U.S. and the U.K. are both readying their next-generation nuclear-powered ballistic missile submarines, the vessels that would launch nuclear weapons from the sea. While both navies are keen to go ahead with these project and replace their aging nuclear subs, British politician Emily Thornberry ruffled feathers recently by suggesting that maybe nuke subs won’t have a place in the future… The other great challenge is power-giving underwater drones the energy for long-duration missions. But there is one type of unmanned submarine which is uniquely well-suited to long-endurance missions. It’s called the underwater glider. Developed by Teledyne Webb in 1991, these gliders are generally about six feet long and resemble a torpedo with wings. Instead of using a propeller, the glider increases its buoyancy and rises slowly, “gliding” forward underwater as it does so. When it reaches the surface, it reduces its buoyancy and glides on a shallow angle downwards. It’s a slow but steady form of propulsion. In 2009, the Scarlet Knight glider from Rutgers University crossed the Atlantic in seven months.