Abstract: Automatic horn warning signal apparatus for use on boats is compact, unitary, self-contained, lightweight, drycell-battery-energized, is manually selectably actuated for automatically sounding any of nine predetermined patterns of warning horn signal sequences applicable to specified, recognized navigational procedures for marine craft. A small motor operates through a first speed-reducing, torque-increasing transmission for rotating a main cam shaft containing nine lobed cams each having a different configuration corresponding to the desired warning signal pattern to be sounded. A control lever is engageable with any of the nine cams for selecting the desired automatically sounded horn signal sequence. A second speed-reducing, torque-increasing transmission rotates a latching cam shaft at one-tenth the rate of the main cam shaft for operating a latch for enabling a pivot bar to serve as fulcrum for the control lever.