Original WWII period Navy ship's "zig zag" clock by Smith. The zig zag clock was designed with an interior ring with adjustable electrical contacts. The minute hand features a flexible metal strip, which, when it touches one of the contact points, sends an electric signal to two terminals at the top of the clock that would be attached to an external bell. The clock is called a zig zag clock because with each bell ring, the ship would alter its course in a different direction to make it less predictable to enemy submarines. Each ship within a convoy would have one of these clocks and they would be synchronized with all other vessels within the convoy. Complete original clocks such as these are not particularly common because the interior rings were often removed to convert them to regular ship's clocks.