Five Letters Mean a Sentence: The Age of the Codebooks Submarine cables charged by the word, so merchants compressed. This guide explains the commercial codebooks, which agreed thousands of sentences in advance and sent each one as a single five-letter code word. Quick facts Motive per-word cable tariffs One code word one full sentence ABC Code from 1874 Bentley's 1906 phrase code Figure codes check letters The codebooks were the century's second code system, layering commerce on top of Morse. Their logic - agree the dictionary first, then send almost nothing - is compression theory in Victorian dress, and their five-letter groups filled the cable ledgers beside the dots and dashes. Start now: morsecodeworks.com Morse Code Works - free Morse code tools and guides. Reference chart