Thompson eventually decided to use the same .45 caliber ammunition in the Thompson submachine gun that he had vetted for use in the M1911 while in the Army. The weapon was patented in 1920, but the major source for contracts had ended with the armistice. Thompson, therefore, marketed the weapon to civilian law enforcement agencies, who bought it in respectable quantities. However, by 1928, low sales had led the company to the financial crisis, and Thompson was replaced as head of the Auto-Ordnance Company.
