The Holy Fathers Navy — Philip Purser

Once she was a light aircraft carrier of the Royal Navy. Now, painted white and manned by a crew of young volunteers, she's a relief ship intended to carry supplies and aid to any stricken area the pet scheme of a lay Catholic order and the source of many jokes about the Pope's battleship. But is the Columba quite as peaceable as she seems? Whose are the unmarked jet fighters that feint an attack on her? What is the true purpose of her last mission in a war-threatened Mediterranean?
Colin Panton, reluctant hero of The Twentymen and Peregrination 22, has been commissioned to make a television film of the venture. He is drawn into a fantastic plot whose roots reach back to the days of the Crusades but whose climax is topical and awesome.