f one Roman galley communicated with another came with the
introduction of cannon as a naval arm. The use of signal-guns was soon
thought of, and war-ships used their guns for signal purposes as early
as the sixteenth century. Not long after came the square-rigged
ship, and it soon occurred to some one that signals could be made by
dropping a sail from the yard-arm a certain number of times.

Up to the middle of the seventeenth century the possibilities of
the naval signal systems were limited indeed. Only a few prearranged
orders and messages could be conveyed. Unlimited communication at a
distance was still impossible, and there were no means of sending a
message to meet an unforeseen emergency. So cumbersome were the signal
systems in use that even though they would convey the intelligence
desired, the speaking-trumpet or a courier was employed wherever
possible.

To the officers of the British navy of the seventeenth century
belongs the credit for the first serious attempt to create a system of
communication which would convey any and all messages. It is not clear
whether Admiral Sir William Penn or James II. established the code.
It was while he was Duke of York and the commander of Britain's
navy, that the James who was later to be king took this part in the
advancement of means of communication. Messages were sent by varying
the position of a single signal flag.

In 1780 Admiral Kempenfeldt thought of adding other signal flags
instead of depending upon the varied positions of a single signal.
From his plan the flag signals now in use by the navies of the world
were developed. The basis of his system was the combining of distinct
flags in pairs.

The work of Admiral Philip Colomb marked another long step forward
in signaling between ships. While a young officer he developed a
night-signal system of flashing lights, still in use to some extent,
and which bears his name. Colomb's most important contribution to the
art of signaling was his realization of the utility of the code which
Morse had developed in connection with the telegraph.

Code flags, which are largely used between ships, have not been
entirely displaced by the wireless. The usual naval code set consists
of a set of alphabet flags and pennants, ten numeral flags, and
additional special flags. This of course provides for spelling out any
conceivable message by simply hoisting letter after letter. So slow
a method is seldom used, however. Various c