According to the book "Science's Most Wanted" by Susan Conner and Linda Kitchen (part of Brassey's Most Wanted series) Brassey's, Inc. Washington, DC, 2002
on page 90 there is a section on the Hale telescope
The Hale
A 200-inch reflector was build in 1948 at Mount Palomar. For nhearly a half-century, the world's most powerful research scope was the Hale on Palomar Mountain in California. The 26-inch thick, 20-ton mirror focused on distant starlight that mere 100-inch scopes could not capture. As a result of the work of George Ellery Hale in 1928, a grant was awarded for the construction of the 200-inch telescope. In 1934, Corning Glass Works in New York developed a special casting technique for the huge Pyrex glass disk. Cooled for eight months, the 20-ton disk was shipped by rail to Pasadena to grind and polish. However, the mirror showed huge optical distortions, which made the telescope almost useless. A second mirror was ordered from Corning, cast in one piece, but because casting had to be done from several melting pots due to the size of the piece, the mirror broke during cooling. A third mirror was ordered, this time from Schott in Mainz, Germany. This was a very delicate job, because the United States was at war with Germany. An agreement between Roosevelt and Hitler made the job possible.
The secret service hid the transport from Mainz to Hamburg. The mirror, yet uncoated, was shipped to San Diego with a warship escort early in 1945 in the last days of the war. A special coating process deposited aluminum uniformly so as not to change the surface shape. It was not until 1947 that the mirror was installed. Only a small engraved plate inside the observatory tells the story.m

Can this be true?