Dive Technologies is a Veteran Owned Small Business with the goal of producing reliable deep-sea Autonomous Underwater Vehicles (AUVs) at a disruptive price point. Our team was tasked with developing a passively actuated “pop-up” antenna for use on their product. The antenna system is critical for communication with the AUV and must completely deploy while it is surfaced. Then it must automatically stow while submerged in order to minimize drag. This mechanism must work without the aid of fuel or electric actuation. Several antenna concepts were developed to actuate using environmental conditions such as drag and pressure. Our final design is a vertically actuating system using a block of deep-sea diving foam and a cantilevered hydrofoil. At the surface, the antenna is extended using buoyant force from the sea-foam. While moving underwater, a hydrofoil assembly at the top of the antenna generates downforce. This downforce overcomes the buoyant force and moves the antenna into a stowed position. The lack of moving parts makes this mechanism easy to manufacture and adjust. The system is fabricated using sturdy 3D printed components and can operate in a wide range of ocean conditions.