His father then sent him to King George V Grammar School, Southport. When he left school in 1940, aged 16, he followed his father into the staff of the Midland Bank as a clerk, working at a branch in Liverpool. He had little aptitude or liking for banking, failing to pass the company's examination in banking theory, and in 1941 he volunteered to join the Fleet Air Arm as soon as he reached the minimum recruitment age in May 1942. He trained as a navigator, was commissioned as an officer, and promoted to lieutenant as a radar instructor. What spare time he had, he devoted to his passionate interest in music. Apart from piano lessons as a child, Culshaw was self-taught musically, and had no ambitions to be a performer. The critic and biographer Richard Osborne wrote of him, "Like many people for whom music is an obsession, Culshaw was a lonely and meticulous person, jealously guarding the sense of personal integrity which his precocious interest in music had helped form and deepen." While in the Fleet Air Arm, Culshaw "wrote articles on music by the dozen and – quite rightly – they came back by the dozen." After many rejections, his first substantial article to be accepted for publication was a piece on Sergei Rachmaninoff, for "The Gramophone", published in March 1945. This led to invitations to broadcast musical talks for the BBC and to contribute articles to classical music magazines. After demobilisation from the forces, Culshaw joined the Decca recording company in November 1946, writing musical analyses and biographies of recording artists for Decca's classical albums. His first book, a short biography of Rachmaninov, was published in 1949 and was well received. The critic of "The Times" praised it for its discriminating judgment, conciseness and discretion. It was followed by two further books; a popular introduction to concertos ("The Concerto" in "The World of Music" series in 1949), and a guide to modern music ("A Century of Music" in 1952). By 1947 Culshaw had been given the chance to produce classical sessions for Decca's rapidly expanding catalogue. At Decca, the musicians whom he recorded included Ida Haendel, Eileen Joyce, Kathleen Ferrier and Clifford Curzon. In 1948 he first worked with Georg Solti, a pianist and aspiring conductor. In 1950, after the introduction of the long-playing record (LP), he produced the first LP versions of the Savoy Operas with the D'Oyly Carte Opera Company.