One of the more surprising stories of cold war US tank development is the M73/M219 machine gun. Developed for use in US armored vehicles, the M73 served most prominently as the coax machine gun in the M48/M60 “Patton” series of tanks and the M551 Sheridan light tank. During its time of service, the M73 distinguished itself as one of the worst machine guns ever adopted by the US military, suffering from numerous malfunctions which lead to frequent jamming. This was particularly frustrating for US tankers who were accustomed to the reliability of the .30 and .50 cal machine guns designed by John Browning which equipped US tanks during WW2 and the early cold war period.
A nice overview of the sad history of the M73/M219 is provided by an article over at the small arms review. The article sums up the M73/M219 saying:
In retrospect, the design of the M73/M219 was an accumulation of novel concepts that should have been thoroughly tested in the application before finalizing the design. The off and on development program challenged the ever-changing design teams with a new learning curve every time the project was restarted. It was a costly program in time, assets, money and loss of face. She was an ugly little baby and somebody should have told her Mama so.
For those interested in primary documents, here is a link to a government report from 1975 detailing tests to find a suitable replacement for the M73/M219. Interestingly, the guns tested include not just US designs, but also the Canadian C1, the German MG3, the MAG58 from Belguim, the British L8A1, the French AAT52 and even the Soviet PKM.
Here is a video showing the operation of the M73.
First Seen at Tank Nut Stan