Original Item: The armed forces of Great Britain were very large users of the Thompson Submachine Gun well before the attack on Pearl Harbor brought the United States into the Second World War. One of their modifications to the Thompson was so good that it is still in use throughout the world, wherever assault rifles are used. This innovation is the use of the assault sling configuration, in which the sling is attached to the TOP of the butt and to the LEFT side of the foregrip. This permits the gun to hang in front of the body in its natural position for use, making it much faster to bring into action and steadier when firing.

To make this conversion, the butt sling swivel was moved to the top (heel) of the butt and the original mortise in the bottom (toe) of the butt was filled with a wooden plate. If the butt did not have the cross bolt at the front, two long wood screws were countersunk into the stock in this location. The exact location of these could vary. A standard SMLE sling swivel was attached to the left side of the vertical foregrip, or, if the Thompson had a horizontal foregrip, the existing swivel was moved from the bottom of the grip to the left side. An additional modification was also made to the butt on most modified guns, which involved drilling a small-diameter hole angled off the main butt trap hole. This additional hole is intended to house the weight of the pull-through.

IMA has obtained a small quantity of Thompson M1-M1A1 BUTT stocks modified by the British during WW2.