We have come across a most interesting document, forming part of The English Historical Review, by Oxford Academic, Philip Williamson, published in 2013, entitled, National Days of Prayer: The Churches, the State and Public Worship in Britain, 1899 – 1957.
It gives much insight as to how National Days of Prayer came about in the UK and why eventually they ceased – the last being in 1947.
In particular, it makes reference to National Days of Prayer during both World Wars and lists no less than 21 days of national prayer on public issues, 1900 to 1950.
You can access the document for on-line reading, by clicking here
Link to article on Oxford Academic website – click here