Examples of commercial signals, including urgent, geographic and code flags.

In the days before radio or other electronic communication, sailors used a code of brightly colored flags to communicate with each other from afar.

For many years, different parts of the world had their own unique set of signal flags, making it nearly impossible for ships from different countries to communicate. In 1855, the International Code of Signals was developed to allow ships whose crews spoke a variety of languages to send messages to one another.

Each flag is intentionally designed with a set of colors that can be easily seen at sea. Signal flag codes are created in red, blue, yellow, black and white. They typically have stark contrasts when colors are placed alongside each other on the same pennant.

Coded flags signify each letter of the alphabet, as well as 10 numeral pennants and a few repeater flags. Ships can send different messages to each other depending on the flags’ design or placement alongside other pennants.

Not only are the first 26 flags each associated with a letter, but that letter also corresponds with a message intended for other ships. For example, a square flag with a yellow triangle and red triangle facing each other on a diagonal symbolizes the letter “O” or “Oscar.” It’s also the international message for “man overboard.” A flag divided in half by white and red vertical rectangles is “H” or “Hotel,” which also indicates a pilot is on board the ship.

The “W” or “Whiskey” flag shows a small red square in the center of the flag, outlined by larger white and blue squares around it. “Whiskey” is an indicator that the ship requires medical assistance.

Ships can also communicate different messages depending on if they hoist a single flag or multiple at a time. Flying a single flag sends an easily recognizable, urgent message, like “man overboard.” Messages become increasingly more detailed when more flags are added.

For example, the combination alpha and Charlie means “I am abandoning my vessel.” Charlie and brave plus the numeral pennant “six” indicates “I require immediate assistance: I am on fire.” Vessels can also ask questions with flags. Echo and lima plus numeral pennant “one” asks another ship, “what is the position of the vessel in distress?”

With each added flag, it became easier to misunderstand or misinterpret a message being sent. Ships would communicate back and forth with answer flags to clarify the message or confirm before any action was taken. Without that clarification, one miscalculation could spell disaster for everyone involved.

Using solely visual communication had its benefits, as it was a silent form of communication and could also be kept flying in the air for long periods of time.

At the same time, these images could only travel so far over long distances. Radio and satellite technologies have made long-distance communication possible in a way that signal flags were never able to achieve.

When these technologies began to replace signal flags, sailors began using them to decorate their ships for special occasions and holidays. International signal flags can sometimes still be seen in high traffic shipping lanes. Their designs remain a vibrant part of maritime culture.