Semaphore

Introduction

The semaphore flag signalling system, designed by the Chappe brothers in France in the late 18th century was used to carry despatches between French army units, including those commanded by Napoleon, and was soon adopted by other European states.

 The semaphore system we use today uses flags, usually square and divided diagonally into a red and a yellow section with the red in the uppermost triangle.
 The signaller, with arms extended, holds the flags in various positions to represent the different letters of the alphabet. There are eight positions for each flag (up, down, out high, low for each of the left and right hands (LH and RH)). For six of the positions (letters H, I, O, W, X, Z see below) the signaller is required to hold one or other of the flags across the body so that both flags are on the same side. The flags, though, are never both in the same position. Although the flags have two different patterns, these are not relevant to the signalling - flags of one colour could be used with the same result.

The full Semaphore alphabet is shown below.

 Exercises Work out the answers to the questions below and fill in the boxes. Click on the button to find out whether you have answered correctly. If you are right then will appear and you should move on to the next question. If appears then your answer is wrong. Click on to clear your original answer and have another go. If you can't work out the right answer then click on to see the answer.

Question 1

 (a) When the LH flag is in the up position, how many possible positions are there for the RH flag? (Do not allow the RH flag to be up as this would mean that the two flags would be in the same position).

 (b) Following on from a), if the LH flag is in the high position, how many possible positions can the RH flag now be in to give new signals?

 (c) Continue this progression to determine the total number of patterns available.

Question 2
What is the total number of patterns if you are allowed

 (a)  6 positions (b)  16 positions

(c)  Why do you think that the 8-position system is used?

Question 3
(a)  Use the semaphore alphabet to send the message H E L P

Use the arrows to move the left and right arms around into the appropriate position.

Right Arm     Right Arm     Right Arm     Right Arm
Left Arm     Left Arm     Left Arm     Left Arm

(b)  Decode the reply ON MY WAY

Right Arm     Right Arm     Right Arm     Right Arm
Left Arm     Left Arm     Left Arm     Left Arm
Right Arm     Right Arm     Right Arm
Left Arm     Left Arm     Left Arm

 Question 4 Decode the words below sent in semaphore. Use capital letters when entering your answer. (a)   (b)   (c)
Just for Fun
Use the semaphore encoder below to create your own messages

Here is some feedback on how you did with questions on this page
 Your overall score for this page is Correct Answers You answered questions correctly out of the questions in this section. Incorrect Answers There were questions where you used the Tell Me button. There were questions with wrong answers. There were questions you didn't attempt.