Nautical flags have been in use since the 1700s. Before there were radios, ships had to be able to communicate with each other over long distances in a way that was clear and easy to see. The communication system also had to be easily understood by anyone on the globe and not be specific to one country or language. By the mid-1800s, those early flags developed into the 40-flag code that is used today.

Location of the Flags

The flag located at the top of the mast indicates the vessel's fleet. The fleet indicates the ownership of the vessel, be it a navy or a private shipping company. The flag of the country the ship sails from (national ensign) is in the place of honor at the end of a gaff-rigged pole under the top of the mast. Signal flags are generally flown from the yardarms -- the outer ends of the pole which crosses the mast.

Types of Signals

Depending on their positioning and number, signal flags can indicate distress, compass points, bearings, ship names, and latitude and longitude. Flown from the yardarms or from the masts in the absence of a yardarm, these flags can be very specific with their messages. Examples of messages include: "Man overboard," "I can't see your running lights," "I need a doctor" and "I would like to enter the harbor." These are all messages which can be signaled using only two flags.

Flag Specifications

Signal flags come in different shapes and colors with varying symbols. There are square flags, one for each letter of the alphabet. There are also 10 numbered pendant flags, and one answering pendant used to indicate a vessel's readiness to receive signals. There are also three repeater pendants, used when a letter needs to be transmitted more than once; for example, for "AA" you would use the "A" flag and a repeater flag. The colors used are the ones easiest to see at sea: the three primary colors, black and white.

Flag Etiquette

When sailing internationally, flags must be changed based on where the vessel is from, where it is going and whether it has cleared customs of the new country. These flags are flown in place of or near the ensign flag. Different countries have different rules about which flags need to be flown when. Flags are also supposed to be used for communication. Avoid flying unnecessary flags; this can cause confusion for those who are using the flag signals properly.

Flags on the Yardarms

The yardarm of a ship is the metal or wooden "arm" which crosses the mast. Ropes are strung from the outer ends of the yardarms to hold the signal flags. Signal flags, or decorative flags, are flown from the yardarms. Other flags indicating country and fleet are found at the top or the mast. For holidays and parades, signal flags can be strung from the waterline at the front of the boat over the masthead and down to the waterline at the back of the boat. When used for communication, they need to be placed in an easily visible spot, flown off the mast from the yardarms.