Abstract: A marine navigational aid system in which at least two marine aids, such as lights, are controlled, such as synchronized, relative to each other without the units being connected with an electrical cable. A marine navigational aid system having an underwater sonic transmitter and receiver for transmitting and receiving coded acoustical signals for controlling navigational aids. A typical installation would consist of a transmitter and a receiver each of which is connected to and actuates a navigational aid. The transmitter sends a complex synchronizing code underwater to the receiver. If the receiver detects and decodes the signal, the receiver is synchronized relative to the transmitter. Both the transmitter and receiver have master clocks which are self-actuated, but the clock of the receiver is controlled and is resettable by a properly decoded signal from the transmitter.