In March of 1932, after years of appeals, Auto Ordnance Corp. finally convinced the Army to adopt their submachine gun as a non-essential limited procurement weapon for use in armored vehicles in the cavalry. Eventually, in 1936 the cavalry changed it from limited to standard procurement. However it wasn't until September of 1938 that the TSMG became officially designated: Submachine gun, Caliber .45 M1928A1. Although the Army orders were important to A.O., the number of guns actually sold were small. A.O. still had some 4,000 of the original 15,000 Colt Model 1921 guns in stock. And the A.O. financial books were in trouble.
By 1939, having undergone a power struggle to gain control of the company, and a resulting change in management, combined with years of sluggish Submachine gun sales, the future of the Auto Ordnance Corp. was bleak. Then, on November 1, 1939 everything changed. The French placed an order for 3,000 Thompsons worth a contract price of $750,000. This was soon followed by inquiries from the British for similar large Submachine gun orders. This meant that Auto Ordnance would finally sell off all of their inventory of Colt guns produced nearly 20 years earlier. To fill these new orders, AO had to build more Thompsons.
Auto Ordnance tried to get Colt to build another order of Thompsons, but was turned down flat. Colt was already committed to building other guns, like the Browning B.A.R. for the Army; but more importantly had not forgotten the bad publicity they received from the misdeeds of gangsters using Tommy Guns bearing the Colt Trademark. So instead, A.O. signed a contract with the Savage Arms Company in Utica, NY to build its Thompsons.
It wasn't long after the French order, that the Second World War created an enormous demand for submachine guns. Between February 1940 and the end of the year, the British placed a total of thirteen orders for 107,500 Thompsons with contracts totaling $21,502,758. In March the French ordered another 3,000 guns, and in December the US Army ordered 20,450. Unfortunately, France fell to the Germans before it could take delivery of the 6,000 guns it had purchased from Auto Ordnance.
Knowing that as the War progressed demand for submachine guns would increase, in August 1940 Auto Ordnance Corp. leased an old brake relining plant in Bridgeport Connecticut and began converting it to produce Thompsons. The first Bridgeport guns came off the assembly line in August 1941; just in time for the Armys largest order yet, 319,000 guns. Although A.O. was assembling Thompsons at the Bridgeport plant, they only manufactured upper and lower receivers. All of the other parts used to build their submachine guns came from Savage and other sub contractors.
By February 1942 Auto Ordnance Corp. had delivered its 500,000th gun. By summer of the same year, the combined output from the Savage and A.O. production lines reached a rate of 90,000 guns a month. Finally in 1944 when TSMG production ended, a total of 1,750,000 completed guns, and spare parts equivalent to another 250,000 guns had been produced. Most of these guns, some 1,250,000, were made at the Savage plant. Savage guns can be identified by the S prefix on the serial number located on the left side of the upper receiver. The remaining guns were made at the Auto Ordnance Bridgeport plant and bear an A.O. prefix.
At the start of the Second World War, the Army finally recognized the need for submachine guns. It also recognized that the Thompson was already obsolete. Compared to German submachine guns, the Tommy Gun was heavier, more complex and costlier to produce. But it did have one major advantage that the Army couldn't ignore. The M1928A1 Thompson was the only submachine gun being mass produced in any Allied country. This alone gave it a huge advantage over any would-be competitors.
Throughout the War, the Thompson underwent design changes that would make it faster and cheaper to produce. The first change eliminated the finely machined Lyman rear gun site. It was replaced with a simple stamped L shaped battle sight; which would later have protective ears added to prevent the sight from be caught up in a soldiers clothing, belts and slings. Next the fancy checkering on the Fire Selector and Safety switches, and Actuator knob was eliminated. The smoothly finished barrel fins were left square cut, and eventually eliminated entirely. However, these changes were minor compared to the changes introduced by Savage.
Savage produced a completely remodeled gun. They eliminated the Blish lock (which had been proven to be unnecessary in a submachine gun) in favor of a straight Blowback design. This eliminated the separate actuator and H piece, and allowed the cocking knob to be mounted directly to the bolt. In this configuration the knob was moved from the top of the receiver to the right side. Other changes were made that: Permanently attached the buttstock to the receiver; Prevented drum magazines from being used; And removed the Cutts compensator. The new gun was standardized in April 1942 as Submachine Gun, Caliber .45, M1. In October 1942 the M1 Thompson was replaced with by M1A1. This version being simplified even further by eliminating the firing pin and hammer. Instead, a fixed firing pin was machined into the face of the bolt.
To make up for the inability of the M1A1 to use the 50 rnd drum magazine, a new 30 rnd magazine was created to replace the standard 20 rnd magazine. The M1928A1 would be able to use either the 20 or 30 rnd box magazines, or the 50 rnd drum. The M1A1 was limited to box magazines only.
An M1A1 could be produced in half the time of a M1928A1, and at a much lower cost. In 1939 Thompsons cost the government $209 apiece. By Spring of 1942 cost reduction design changes had brought this down to $70. In February of 1944 the M1A1 reached a low price of $45 each, including accessories and spare parts. But by the end of 1944, the M1A1 was replaced with the even lower cost M3 Grease Gun.