In just about every war since WWII soldiers have found fast-firing anti-aircraft guns to be extremely effective against…infantry.
In WWII the Americans nicknamed their M45 Quadmount — four 12,7mm machine guns designed for air defense — “meat chopper” and “Krautmower” for its utility in fighting enemy foot soldiers.
In Afghanistan and Chechnya one of the most beloved weapons of the Soviets/Russians was the Shilka. Not bad for an anti-aircraft weapon in a war where the opposing side didn’t have an air force.
Designed as an air defense weapon (it even came with its own radar dish) the Shilka was very lightly armored for Afghanistan, but its four 23mm autocannons offered more useful firepower than either the potent, but slow, tank guns, or the single autocannon of the BMP-2 infantry carrier. Also it was the only Soviet weapon whose guns had sufficient elevation to easily fire on targets in the hills from valley floors.
In Bosnia, one thing all side could agree on was what a crappy (and scary) thing it was to be fired upon by the Czech-made M53 Praga (Prague). Praga was a twin 30mm autocannon mounted on the back of a lightly armored truck.
As it was an anti-air weapon the gunner was actually completely unprotected, but seeing it out-ranged all but the heaviest direct-fire weapons that wasn’t much of an issue. It could stop enemy attacks just by mowing down trees the enemy was moving through, arranging for a hellish rain of falling trunks and branches and exploding bullets.
Despite proving their worth in an anti-infantry role over and over again however, for some reason no military of any nation ever asked for a dedicated anti-infantry weapon system based on multiple autocannons be developed. The anti-aircraft systems had the requisite firepower but they were too lightly armored. Ideally an anti-infantry vehicle carrying such weapons would be much heavier and better protected.
Enter the BMPT. In the late 1990s Russia’s Uralvagonzavod (the most famous Russian tank-maker) acting on its own did what should have probably been done decades ago. It mounted a turret sporting twin 30mm autocannons on the chassis of a T-72 tank.
The cannons are capable of high elevation, the turret is unmanned for extra crew survivability, the vehicle comes with four guided anti-tank missiles giving it decent tank-hunting capabilities, and its modern explosive reactive armor makes it one of the best protected vehicles in the world.