For its 150th anniversary in 1926, Congress authorized a gold Quarter Eagle and a silver Half Dollar to celebrate the signing of the
Declaration of Independence; it did the same for the 200th Anniversary in 1976 via new designs for the quarter, half dollar and dollar struck in 1975-76. So, why not a commemorative half dollar for the 175th anniversary in 1951?
In April 1951, William Thomas Granahan (D-PA) introduced a bill in the House of Representatives that called for the "coinage of special 50-cent pieces in commemoration of the one hundred and seventy-fifth anniversary of the signing of the Declaration of Independence." The half dollar was to be of standard specifications and be struck for circulation "in such numbers and in such design as the Secretary of the Treasury may deem appropriate."
Considering Granahan's connections to Philadelphia - he was born in the city and represented Pennsylvania's 2nd District in the House (Pennsylvania's 2nd District includes portions of Philadelphia) - it isn't much of a surprise that he would be the one to introduce a bill that looked to commemorate a seminal document of US history that was debated and signed in Philadelphia.
The bill did not include any language regarding which Mint facilities could be used or the period during which the coins could be struck. It seems likely, however, that Philadelphia, Denver and San Francisco would all have been employed to strike the coins during 1951.
The bill was referred to the Committee on Banking and Currency but was not reported out. Though no Hearing was held on the coin proposal, I imagine that one of the obstacles in the way of the coin's passage was an objection by the Treasury Department. The new Franklin half dollar had just been released in 1948, and was the third half dollar design in regular circulation at the time - the Franklin half dollar had the same silver weight and composition as the preceding Walking Liberty and Barber half dollars and circulated alongside of them. I can imagine the Treasury Department not being in favor of adding yet another half dollar design to the US' coinage system.
As no companion bill was introduced in the Senate, the inaction on the House bill marked the end of a potential circulating commemorative half dollar that would have marked the 175th anniversary of the signing of the
Declaration of Independence and been a nice bridge between the coins of 1926 and 1976.
An attempt was also made to secure a commemorative US postage stamp for the 1951 anniversary - it failed as well.
Though a commemorative coin was not authorized, the US Congress did vote to create a Commission to assist Philadelphia with its plans for the 175th anniversary. So, the milestone did receive official Federal recognition.
For other of my posts about commemorative coins and medals, including more What If? stories, see:
Commems Collection.