And now I understand where the substitution phrase “catch a tiger by the toe” was chosen! 
As to ‘consonant vowel pairs’ Japanese Morse Code equivalents for telegraph and wireless corresponded to kana, each of which is a consonant/vowel pair, Japanese doesn’t have letters. So any signal in Japanese was composed of consonant/vowel pairs.
The Japanese Wikipedia entry for ‘tora tora tora’ gives acronym for TOtsugeki RAigeki (sudden attack, lightning attack) and the word tora (‘tiger’) as possible origins. IOW it doesn’t seem at this point it will ever certainly be known, or it was both, or meant one to some people and the other to other people, or simply what they were supposed to signal if surprise was achieved.
Note that the entry is under トラトラトラ which is katakana. The IJN though used katakana a lot for abbreviations and codes, so perhaps in that sense it leans towards saying ‘it’s just a code’. For example the action reports of IJN units (those of the carrier air groups at PH for example) are written in an abbreviated style consisting of Chinese characters (for people’s names and some common nouns and verbs, as in normal writing now, though older forms of them not the simplified postwar ones), certain IJN-only symbols (for various a/c types for example, based on stylized Latin letters), and katakana for everything else. In normal Japanese writing now, katakana is generally used only for foreign words, and hiragana for grammatical particles, etc.
Side question: Was this portrayed in an old British film? Because what you say about the dog’s name and it dying in a car accident is exactly what was being portrayed in an old film on a TV set in the background of the hotel room that Bob Geldof decided to trash in Pink Floyd: The Wall (1982). Really.
Yes, the dog’s name was mentioned several times in the 1955 film The Dam Busters.
Thank you. I’ve seen Pink Floyd: The Wall many times over the years and have always wondered what old movies that was.
I wonder whether taking the first 2 syllables of the long words to form “Tora” is related to a common type of abbreviation and word formation in Japanese?
They do this with English words like “Pocket Monster” becoming “Pokemon” or “Costume play” becoming “Cosplay” and “personal computer” becoming “pasocon”.
And this also happens with Japanese words, like Tokyo Daigaku (Tokyo University) becoming Todai.
Of course we do this in English (like University of Connecticut becoming UConn) but it seems more common in Japanese.
It is very common in Japanese to take the first two kanji – not syllables – of words for an abbreviation.
However, it’s much more likely that tora tora tora was simply the code used.
I think that was just the Germans who lost a few letters… and the Russians.