In 1932, the navy purchased its first offensive capacity, two Hawker Horsley torpedo bombers with an option to produce a following series on the Orlogsværft. After four years of testing and practice, the naval air service had agreed to expand the offensive capacities with the Horsley, but at this time funding from the Danish government had been cut and no further torpedo bombers were acquired. In the late 1930s the government changed plans and increased the budget for military purchases following the German expansions in central Europe. In 1938, 12 Fairey P. 4./34 were to be produced at Orlogsværftet along with 12 Italian Macchi MC-200 fighters. None of them were ever produced before the German invasion of Denmark at April 9, 1940.

Based on the above article, answer a question. How many years after 12 Fairey P. 4./34 were to be produced at Orlogsværftet along with 12 Italian Macchi MC-200 fighters did the German invasion of Denmark occur?
2