Ironically, Reynolds' primary function in the aircraft industry was as a a supplier of extruded, structural components made from a high strength aluminum alloy known as Hiduminium (HIgh DUty aluMINIUM). They had diversified into Hinduminium products in 1934 and set up a separate factory for their production. Cyclists always think of steel when they think of Reynolds but they were big into aluminum for the aircradt industry. It would be interesting to see what would have happened if they had extended their experience with aluminum into the bicycle frame field.

Another British bicycle tubing manufacturer that was big in the aircraft industry was Accles & Pollack. Their butted CrMo tubing actually came out prior to Reynolds 531.

A. L. Colombo (manufacturer of Columbus tubing) is also known to have manufactured aircraft tubing.

It wouldn't surprise if most of the bicycle tubing manufacturers were involved in aircraft manufacture during World War II. Once the war started, the supply of high strength alloys would have been diverted to the war effort and the companies' experience in drawing tubes with these alloys would be both vital to the war effort and profitable. Tange goes back to the 1920s. Ateliers de la Rive (Vitus) was formed in 1931 and Mannesmann of Germany was producing seamless tubing as early as the late 19th century. Conceivably, they were all involved in war efforts. To not participate would have made it very hard to survive.