I'm reading some letters written to FDR circa January 1945. One person complains about "furlough specials." Here's the phrase in context: “My heart (and many other hearts) were filled with resentment at the time of your son Elliott’s recent marriage—‘chartering planes’ etc. when our own sons were riding ‘furlough specials’ thousands of miles in order to visit their families before leaving the United States.” I have not been able to figure out what exactly this correspondent meant by "furlough specials." She seems to be insinuating some inferior type of accommodation. Can someone give me insight into this slang? If you cannot verify your response but have a good sense feel free to pm me, so as to not break the subreddit rules.
They're not planes, but trains instead. They were coaches/cars attached to regular trains specifically for soldiers on leave. They would have been cramped and unpleasant, compared to chartering a plane or even regular train travel. For more information, see pages 58-64 of this book, an official history of the US Army Transportation Corps.