In keeping it simple I would bring a few batteries of light artilley. Very simple Arty like an Ig-18. 75mm and very mobile.
It works as simply as a break open shotgun. It is made for direct short range infantry support so it would be great in this role.
Training would be minimal. Loader could be anyone trained to do it fast. Gunner could be trained very quickly and easily. The gun commanders and battery commanders would need a level of training but this would still be quick for the job needed.
Massed thay could provide area denial to masses ranks. The gun is mobile enough to be moved by it's own crew and not need much horse support.
The accuracy would be devistating compaired to the artillery of the day despite it's smaller caliber.
Training time, 1 month and they would dominate the battlefield. Not the greatest weapon, but likely to be accepted and easy to train on and use. Made for this role so it should work well.
Specs.
The leIG was primarily effective against “soft” targets such as; troops, buildings, fortified positions, and vehicles. The leIG was capable of firing on tanks, however, it produced mixed results. The “blast” area was quite effective against the soft targets. The standard High Explosive round could produce an impact resulting in a 30 yard wide by 10 yard deep “kill zone” with large fragments traveling as far as 150 yards. The armor piercing rounds were capable of penetrating up to 90mm (3 ½ inches) of armor plate at close range
Optics/sighting devices: The gun was aimed by using a visible aiming device with an independent sight line and parabolic scope. This gave a four-fold magnification of a ten-degree field of vision.
Gun shells:
7.5cm IG shell 38 HL/A Armour-piercing 75mm penetration
7.5cm IG Shell 38 HL/B Armour-piercing 90mm penetration
Combat range against tanks: 2000 meters
Shell type
Inf. shell 18 5.45 Kg
Inf. shell 38 HL/A 3.1 Kg
Inf. Shell 38 HL/B 3.5 Kg
Range of Shells:
7.5cm IG shell HE 3500 meters
7.5cm IG shell special 4600 meters
Some Russian troops with captured guns to show size.