POW: Irish Code
Frank and Eileen had met in 1929 when they were both learning Irish in the Gaeltacht area in Donegal. Frank was fond of using phrases in Irish in many of his letters to Eileen. Often these were just terms of endearment but towards the end of the war, from June 1944 onwards, he used Irish written in the old-fashioned Gaelic script to hide information in case the letters were seen by the Japanese; sometimes he just wrote in English but used Gaelic script to hide specific words or phrases. Frank would have been taught Irish with the use of Gaelic script at school as it was in common use in Ireland until the mid-20th century.
As a POW the unusual script provided a convenient way to disguise his writing when needed. The prisoners had access to a clandestine radio as well as stolen Japanese newspapers and so they were being kept up to date about the progress of the war with the obvious boost to morale. For example, they knew about D-Day and the death of Hitler within a day or two of these events happening. Frank was always worried that his diary would be discovered by the Japanese and that is why he decided to hide the implied existence of the radio by writing key pieces of information in Irish. The transcript has some examples of his Irish writings along with translations and some context. (I am grateful to Angela Flynn and her mother as well as my cousin, Roisin Scullion, for providing translations.)