Any extensive use of the International Code flags will call for the use of International Code of Signals, published by the U.S. Naval Oceanographic Office. A few of the principal signals and the general method of making and answering signals are given here.

HOW TO MAKE A SIGNAL. If you want to make a signal, hoist your ensign with the code flag under it. If more than one vessel or signal station is in sight and your signal is intended for a particular vessel or signal station, indicate which vessel or signal station you are addressing by making the distinguishing signal (i.e., the signal letters) of the vessel or station with which you want to communicate. If you don't know the distinguishing signal, observe that ships will answer with their distinguishing signal hoists or answering pennant.

When you have been answered by the vessel you are addressing, proceed with your signal, first hauling down your code flag. It may be required for making or answering signals.

Signals should always be hoisted where they can be best seen, not necessarily at the masthead. Each hoist should be kept flying until the other ship hoists her answering pennant close up. When finished signaling, haul down your ensign.

HOW TO ANSWER A SIGNAL. On seeing a signal made by another ship, hoist your answering pennant at the dip. (A flag is at the dip when it is hoisted about three-quarters up its halyard.)

Always hoist the answering pennant where it can be seen best.

When the hoist has been recognized and is understood, hoist your answering pennant close up, and keep it there until the other ship hauls her hoist down. Then haul your answering pennant down to the dip and wait for the next hoist.

If the other ship's flags cannot be made out or the signal is not understood, keep your answering pennant at the dip, and make a signal to that effect. When she has repeated or clarified her signal, hoist your answering pennant close up.

This method of signaling is an old favorite of the Navy and has much to recommend it. It is the fastest way of sending messages by flags. It can be used only in the daytime and at short distances. Form the letters by placing two flags at certain angles to each other. Hold each so that the staff is a continuation of your forearm. Keep your arms stiff.

Whenever you cross a flag in front of you to make a letter, twist your body slightly in the same direction.

To send a semaphore message, get the receiver's attention with the Attention signal, made by waving both flags repeatedly overhead in a scissor-like motion. When the receiver sends the letter K, you can go ahead.

Send the letters of each word by going directly from the position of one letter, without stopping, into the position of the next, pausing in each. If you have to think of the next letter, hold the letter you are making until the next one comes to mind.

To indicate the end of a word, give the front signal by bringing the flags down in front of you, with the staffs crossing each other.

Whenever double letters appear in a word, use the front signal to separate them. Make the first letter, then front, and immediately, without pause, bring the flags again in position of the letter.

The receiver acknowledges each word by sending C. If he or she suddenly sends I-M-I, it means that he or she did not catch your last word. Repeat it and continue from there. If you have made an error yourself, send eight Es and start again from the beginning of that word. Finish the message with A-R and wait for the receiver to make the letter R. This means the receiver has your message.

The Morse code is standard throughout the world. It is possible to send Morse code by several different methods: it is easily simulated by a simple electric buzzer; it may be signaled by the ship's whistle, siren, or foghorn; or it may be transmitted by signal flag when the flag is held erect for a long interval for dashes and a short one for dots, or, more commonly, swung to the sender's left for a dash and to the sender's right for a dot. It is also sent with a blinker system.