The 51-foot-long, yellow and grey autonomous undersea vehicle is being designed to glide just beneath the waves or along the ocean floor for months at a time with little to no contact with human operators. Boeing has said Echo Voyager can reach a maximum depth of 11,000 feet, with a top speed of about 9 mph. The drone runs on a hybrid electric-battery/marine diesel system; its diesel generator will kick in when the battery runs low. It periodically resurfaces to snorkel depth to recharge.