Invasion forces of the russian army are moving old T-54/55 tanks to the frontlines in Ukraine. Most likely, these artifacts will play the role of stationary firing points dug into the soil but there's still a chance some of them may encounter a Ukrainian T-72. Although there is an obvious technological gap between these combat vehicles, the outcome of such hypothetical combat is not carved in stone: besides the capabilities of the equipment, the preparedness of the crew and situational awareness will be no less important.
For illustration, it looks relevant to recall the tank battle that happened between the T-55 platoon and the T-72A platoon of the Romanian Army on December 24, 1989, during the revolt in Romania that led to the overthrow of the Ceaușescu regime. A single T-55 hit the T-72A with five shots of 100mm caliber, there was no backfire, and inthat situation the tanks' specifications did not matter as much as expected. This might be the only known case of a T-55 clashing against a T-72, so we decided to break it down.
Read more: Why Digging T-54 or T-62 Into Ground as Stationary Firing Point is Not As Simple As it Sounds
First, we should clarify the context. The T-72A at the time of the Warsaw Pact was considered a 'secret tank' in the Romanian military. All 30 vehicles of this type were in a single secret tank battalion belonging to the elite Vlad Țepeș Regiment.
The Ceaușescu regime provided their T-72As with sufficient ammunition supply but instead took care that their crews were loyal to the party and the government. In the meantime, most of the Romanian military only saw T-55 tanks or even T-34-85.
During the revolution, in December 1989, the Romanian military initially received an order to operate in the 'anti-terrorist operation' mode, that is, to destroy "terrorist tanks" captured by common citizens that allegedly planned to open fire on military facilities.
On the other hand, the forces opposed to the Ceaușescu regime were expecting the USSR to certainly send its military force to save its satellite in the Communist Block. So the rebels were confident that russian tanks were already on Romanian territory, and they had to shoot them down.
That is why the crew of a Romanian T-55 did not hesitate to open fire on the T-72A since they took it for a russian tank. Five hits with 100mm rounds landed: three HE-FRAG and two shaped-charge BK-412 AP-HEAT shells. Damage was caused to the antenna and the fuel tank, the back armor plate was dented, and the two armor-piercing rounds hit the engine section.
There was no fire back from the T-72A. Still no one knows why: the crew either received no ammunition or simply decided to retreat. Soldiers inside the T-72A survived the series of five hits and fled the vehicle. After a while, the tank was repaired and put back to service.
Fair to note, the Armed Forces of Ukraine also nowadays fight off russians with T-55 tanks – to be exact, the modernized M-55S version of it received from Slovenia. The fact these vehicles were modernized is significant: the 100mm gun was replaced with the 105mm L7 facilitated by the digital fire control system.
The 105mm tank subcaliber penetrator used by L7 can pierce through 450 to 500 millimeters of homogeneous armor (compared to over 550 mm for the best modern ammunition). On the other hand, the standard T-55's D-10T2S gun firing the 3UBM11 created back in the 1970s, can only pierce through 300 mm.
All the tanks used by the Ukrainian Army help drive off russian invaders from the territories of Ukraine, so the combat between an M-55S and the enemy T-72 is not something to be ruled out. If only russians don't run out of T-72s before that happens.