The Fort Peck Memorial Association attempted to join the commemorative coin craze in January 1937 when its bill for a coin to mark the completion of the Fort Peck Dam in Montana was introduced in Congress. As many collectors (and dealers) were still very active in the commemorative market, notification of the new bill caused the Memorial Association to receive numerous inquiries regarding the status, pricing and availability of the coin.
As they were almost certain of the passage and approval of their commemorative coin bill by Congress and President Roosevelt, respectively, they decided to place an advertisement in the March 1937 issues of the
ANA's
The Numismatist to provide the collecting community with everything they needed to know about the potential new coin. (The ad is presented below.)
Unfortunately for them, Congress was quickly cooling on the idea of commemorative coins -- Roosevelt had actually been opposed for several years -- and the Fort Peck Dam half-dollar was not to be. As noted below, the Fort Peck Dam was "the Largest Earth Filled Dam in the World" at the time of its construction -- it's still the largest in the US; the Tarbela Dam in Pakistan is currently the largest earthen dam in the world. The Dam's construction/completion was certainly an accomplishment worth noting -- just not with an official US coin.
The Association was forced to return the monies collected from interested collectors when the coin's bill died in committee and it became clear that it would not be successfully resurrected.
One note about the timing of the proposed commemorative...The coin was planned for 1937 based on initial construction schedules. The dam was not completed until 1940, however. While some construction delays were due to the number of technical issues that needed to be resolved "on the fly," the largest issue was the major earth slide that the dam suffered after it had been closed and nearly completed; the slide occurred in September 1938 -- eight men died in the accident. Construction was halted until the failure could be studied and it could be determined if the dam could be safely completed. Eventually it was decided to move forward with the dam's completion and the last load of earth was dumped on 11 October 1940. Here's a link to learn more about the Fort Peck Dam:
http://www.fortpeckdam.com/Advertisement for Fort Peck Half-Dollar (The Numismatist, March 1937).