It was the first anti-tank gun to adopt a smoothbore barrel, and to introduce modern armor piercing shot, like the APFSDS.

The T-12 served as the primary towed anti-tank artillery in the Soviet and Bulgarian armies from the early 1960s to the late 1980s.

The T-12 was designed by the construction bureau of the Yurga Machine-Building Plant as a replacement for the BS-3 100 mm gun.

[3][4] The T-12 was typically deployed in the anti-tank units of armored and motor rifle regiments to protect flanks against counter-attacks during rapid advances.

[5] By the mid-1990s, modern western tanks' frontal armor protection could no longer be penetrated by a 100 mm gun.

On introduction, the T-12's gun differed from all existing artillery by employing a smoothbore barrel instead of a rifled one.

The reasons to introduce a smoothbore barrel primarily relate to armor piercing shot.

It is most effective if it has the form of a long narrow diameter rod fired at very high speed.

In flight it can be stabilized by a rifled gun barrel having given it rotation when it was fired, but this becomes less effective if the projectile becomes longer.

[8] This started the replacement of the armour-piercing discarding sabot (APDS) fired by rifled guns by the armour-piercing fin-stabilized discarding sabot (APFSDS) shot fired by smoothbore guns.

[7] High-explosive anti-tank (HEAT) shells do not rely on high speed to penetrate armor, but on the explosion of the projectile on impact.

The problem of using a rifled gun to fire a HEAT shot was that the stabilizing spin degraded the penetrating power by as much as half.

Therefore, the 115 mm U-5TS gun of the T-62 was developed with a larger caliber, so it could use more propellant while not requiring the very long T-12 projectiles.

During the War in Donbas (2014–2022), the Ukrainian army had 500 anti tank guns of the types T-12, MT-12 and MT-12R.

However, in January 2023, the BBC published an article and video showing the use of a T-12 by Ukrainian forces near Bakhmut.

During the May 2023 Belgorod Oblast attack it was confirmed on the front line, because a piece was destroyed together with some trucks.

[27] Incomplete, and still requiring thorough check whether T-12 or MT-12 was used: In August 2022, videos of a Ukrainian T-12 mounted on top of an MT-LB began to circulate online.