Hi, im new to this forum, i wanted to ask a few questions about my M1A1 Thompson. First, what does a T on the end of serial number stands for, i could not find any other example of that weapon with it, second, it does not have the Property of US Gov’t markings, can anyone answer my questions?

How about some close up photos of all markings?

Civilian or law enforcement firearm.

There was a “T” serial number pre-fix for the experimental, prototype of the M3 grease gun. Of course, those were made on a larger scale by a completely different manufacturer- “Guide Lamp”, which was a pre-war headlight manufacturer branch of General Motors in Anderson, IN. 
 

The M3, replacing the Thompson due to cost and weight, was a $17.50 sub machine gun, which apparently translates to $280 in today’s dollars.

 

Having shot both, I actually prefer the M3, as it has a slower rate of fire and, unlike the myths, is quite easy to control. There is little “walk” as the bolt assembly is MASSIVE for a gun that is otherwise stamped sheet metal. 
 

Your Thompson is a Cadillac, while the M3 is a Chevy Nova. 

If you can post shots of the markings on the receiver (both sides) i and get some folks in another forum to help

Reising SMG a pleasure to shoot but much lighter than TSMG . 

The Grase Gun is also great to shoot.  

On 1/14/2026 at 12:42 PM, BT3_Guns said:

The Grase Gun is also great to shoot.  

It is-

 

For some reason, people who have not shot them perpetuate the myth that there was considerable vertical “walk” when firing. There is very little, as a matter of fact, and due to the weight of the bolt, the first shot tends to be low, not high. 
 

The grease gun, given that one grips it on the mag well, is actually much easier to control than a Thompson. 

Yes, the Tommy Gun does have more walk especially if you just spray & pray.  I find that with a bit of practice and trigger control I can consistently get a 3-round burst in a 3-inch circle.  When the Marines first tested the Thompson, their AARs discussed the need for burst fire.

 

Having shot both, I find the Grease Gun more easily controlled especially if you cannot get to the range regularly.  That said, I will always pick up the Tommy Gun first - just my personal preference.