Recent technological advances in manned and unmanned undersea vehicles have overcome some of the limitations of divers and diving equipment. Without a vehicle, divers often became sluggish and their mental concentration became limited. Because of undersea pressure which affected their speech organs, communication among divers was difficult or impossible. But today, most oceanographers make observations by means of instruments which are lowered into the ocean or from samples taken from the water. Direct observations of the ocean floor are made not only by divers but also by deep-diving submarines. Some pf these submarines can dive to depths of more than seven miles and cruise at depths of fifteen thousand feet. Radio-equiped buoys can be operated by remote control in order to transmit information back to land-based laboratories, including data about water temperature, currents, and weather.