The US Army made the T5 halftrack in the late 1930s to tow the 75mm Pack Howitzer. The Army had done a study that showed horses actually took up more shipping space to deploy overseas than motor vehicles.
As a result, they began to modernized and motorize the Army. Horses still played and important role in the Army for scouting and patrolling the Mexican border.
The intention was to motorize the support roles. Rather than have six horses towing artillery they would use one caterpillar tractor, halftrack, or truck.
The other advantage is motorized vehicles are faster than horses, particularly on roads. However, wooden wagon wheels can't be towed by motor vehicles at speeds faster than about ten miles per hour. The rigid nature of wooden wheels causes them to bounce over every small bump, eventually creating an oscillation that will flip the artillery and often the vehicle as well.
So the Army began upgrading their artillery from spoked wooden wheels, to pneumatic rubber tires. Due to the tiny budget the project took years to accomplish and was never even close to finished by the start of World War Two.
The US Army had thousands of French 75's, and British QF 18-pounder guns that were made in the USA, rechambered to use French 75 ammunition and they were still working on them when Japan invaded the Philippines. Most of the artillery in the overseas possessions was the M1917, the 75mm based on the British gun.
By the time of Pearl Harbor most of the guns in the USA were changed over to rubber tires, but those overseas were not. Even many in the National Guard were mostly changed over.
Here is the T5 with the machine gun mounted toward the front.
Machine gun and towing the pack howitzer.
While the halftrack was intended to tow the 75mm pack howitzer, Cavalry Divisions also had 37mm anti-tank guns and there is no reason why the T5 could not be pressed into service to tow those.
The T5 deployed with machine gun, and an anti-tank gun and pack howitzer.