Too Important

During WWII gliders were often important in various types of actions. They were quiet, they could land in short, unprepared fields and they were disposable and therefore - at least presumably - cheap. Being build of wood and fabric they used materials less in demand for the war effort. Also, with engines often in short supply, using an actual airplane to tow a glider roughly doubled how much could be moved with the same engines. At some point it struck someone that the planes which towed the gliders had characteristics similar to those of the gliders and were already being mass-produced. What if, instead of the painstaking, time-consuming process of getting a special contract for a new design they simply could modify tired transport planes? This would even be cheaper than the disposable gliders, and use little in the way of vital materials, since the planes were already built!

One experiment was to take a C-47 (the US military transport version of the DC-3) remove the engines, fair over the nacelles and test it as a towed glider. The XCG-17 proved to have better handling and a better glide ratio than any of the more common purpose-made gliders. And the "donor" plane was being pumped out by the thousand.

However, the C-47 and its cousins were so important to the war effort that the only ones not still being flown were too damaged to convert to gliders.

Which is a bit of a shame, since the C-47s were also sturdier than the purpose-built craft and could have saved the lives of many men lost when their wood and cloth gliders broke up during hard landings or due to encountering obstacles during landing.