Signallers' logs, being official documents, had to be perfectly legible - with no alterations. If we missed a letter, due to interference or a momentary lapse of concentration, it was tempting to guess what it might have been by the context. However, guessing what the missed character might have been was forbidden; we were told that operationally it was totally unacceptable because the originator of the message, unknown to the operator receiving the message, might have deliberately misspelled a word for security reasons or as part of a cipher. World War 2 memories, no doubt.
After we had worked our way through all 49 punched tapes, the instructors reverted to sending the code manually and then they would occasionally misspell words deliberately, or introduce grammatical errors, to catch out any of us who were tempted to read ahead. A missed letter counted as one error but a wrong letter written down counted as two errors - and just a few of those made all the difference between a pass and a fail. At speeds above about 20 words per minute there was no time to make corrections anyway: if you had second thoughts about what the missed character might have been, spending time thinking about it merely meant that you missed the next few characters - and almost certainly failed that test.
There were a number of curious aspects to writing down Morse code sent at more than 20 wpm that I and several others on my course used to ponder. I remembered that at junior school when we first started having dictation lessons, I soon got into the habit of not writing each word down as soon as I heard it, as some of my fellow pupils did. I delayed writing anything down until I had heard several words because I found that my handwriting was then much neater than those who scribbled each word as they recognised it. In the RAF it was mandatory to take plain language down in 'joined up' writing. One day, towards the end of the course, when I was writing down some plain language high speed Morse code, I realised that I was instinctively letting my writing lag the transmission by anything up to six characters. It seemed to make it easier to do the 'joined-up' writing. I also noticed that after writing down a long passage of high speed Morse, I had not the least idea of what I had written. In other words, as I used to say, "The Morse wrote itself down without any help from me". It really did seem like that. One of my instructors told me that was the sign of a good signaller.
Some of our eastern European civilian instructors, those who had served as wireless operators during WW2, used to lapse into a variety of foreign languages in the middle of a passage of English, and sometimes they included a sprinkling of accented letters and occasionally some Cyrillic letters, none of which we had been taught. I was not always aware of this until the end of the test when I had time to read over what I had written and found a number of blanks where the unfamiliar letters had been transmitted. Actually, they were not blank spaces because we were required to pencil a dot on our log to indicate each and every missed symbol. One of the instructors was a former Polish Air Force signaller and when he lapsed into Polish Morse code there was absolutely no way we could have read that ahead. We used to get our own back on him by cheekily pointing out that his pronunciation of the English language left a lot to be desired, even though he had worked for the RAF for many years.
That leads me to two small digressions. The international distress signal when sent in Morse code is not, as most non-telegraphists think, the letters SOS. To be strictly accurate, and pedantic, 'SOS' is a single symbol made up of three dots-three dashes-three dots. It was introduced first by Germany in April 1905 and internationally the following year. Apparently the nine-component SOS symbol was chosen by Germany because it was long enough to ensure that it could not be confused with any other, and it was also very easy to remember. Only later did someone suggest that SOS was an acronym for Save Our Souls. Perhaps that someone was an Englishman who wanted to get his own back on the French who had already coined M'aidez as the voice equivalent of SOS - that later became Mayday in English speech and writing.
The second digression concerns the Marconi Maritime Company. Their communicators used CQD as the Morse code distress signal from 1904 until as late as the Titanic disaster in 1912. CQ was, and still is, the recognised Morse signal for "Calling all stations"; the added D indicated that the transmitting station was in distress. In the 1997 film Titanic, one of the wireless operators refers to the 'new' international distress signal SOS being in use - a nice touch of authenticity that probably only wireless operators watching the film notice.
I passed official tests sending and receiving Morse code at 25 words per minute. On a good day I could read 30 words per minute when the Morse was sent by machine rather than by the hand of an operator. Incidentally, because the Morse keys in aircraft were usually positioned to favour use of the right hand, I found that being a left-handed writer was a distinct advantage. In flight I used to write with my left hand and transmit with my right hand – often both at the same time! Although I have not needed to use Morse code now for several decades, I discovered a few years ago that I could still read it at about 20 words per minute but I could no longer write it down at those speeds because my pen hand no longer works that fast. However, I could type Morse code straight into a word processor at 20 wpm using two fingers and a thumb on each hand, but that’s another matter.