Editing Optical communication (section)

=== Semaphore signal flags ===
{{Main|Flag semaphore}}
[[File:020118-N-6520M-011 Semaphore Flags.jpg|thumb|A naval signaler transmitting a message by flag semaphore (2002).]]
Semaphore flags are the system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags, objects or arms; it is read when they are in a fixed position.

Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms of [[semaphore line|shutter semaphores]]) in the maritime world in the 19th century. They are still used during [[Underway replenishment|underway replenishment at sea]] and are acceptable for emergency communication in daylight or, using lighted wands instead of flags, at night.

The newer flag semaphore system uses two short poles with square flags, which a signaler holds in different positions to convey letters of the alphabet and numbers. The transmitter holds one pole in each hand, and extends each arm in one of eight possible directions. Except for in the rest position, the flags cannot overlap. The flags are colored differently based on whether the signals are sent by sea or by land. At sea, the flags are colored red and yellow (the [[International maritime signal flags#Letters|Oscar flags]]), while on land, they are white and blue (the [[International maritime signal flags#Letters|Papa flags]]). Flags are not required, they just make the characters more obvious.