Flag semaphore uses a combination of basic strokes to roughly form katakana characters. Within 800 meters, they were able to transmit up to 55 characters per minute.

Basic Stroke 0

Basic Stroke 1

(Reverse)

Basic Stroke 2

Rest

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Japanese semaphore strokes used for signal transmissions.

Reference to "Naval Warship Mechanisms Encyclopedia: Japanese Destroyers", Wikipedia article on semaphore flags, etc...

Basic stroke 13

Basic Stroke 14

Reverse

アイウエオ - A I U E O Japanese alphabet in katakana characters

カキクケコ　Ka Ki Ku Ke Ko

※The Naval Warship Mechanism Encyclopedia did not list the the reverse on the second stroke for エ(E).

The Navy and the Army's flags were shaped differently. The Navy's flag had handles. Although I couldn't find sources with clear confirmation on the Army flags, I have received information that the Army flags were carried the way Maruyu is holding to the right. Until 1921, there were Army semaphore flags elongated horzontally used for aviation purposes.

These two types goes by shape, and are easy to understand!

You probably got the right answer if you found the dakuten by listening to my four letter advice, and saw where I began each line.

Su and Ne are exceptions. They're based on 寸 and 子.

Waves until a response is given.

Once they are ready to decode.

Send once they acknowledged the signal.

Acknowledged

One rotation