This boat was a pre-war design, specifically built to operate on numerous Soviet rivers. It used parts from the T-28 medium tank heavily, including turrets and engine. When that tank went out of production, boat was redesigned to use T-34 main turret instead, while keeping machine-gun turrets and engine of T-28. During the war T-34 turrets were mainly recovered from destroyed tanks, since new turrets could not be allocated for boat production.
BKA-1125 is fully armored. Hull is only protected against small arms, however main turret retains its medium tank armor level, and low profile makes it quite hard to hit.
Main role of this craft is support of ground troops, and generally it can be considered a river-going tank.
The boat has no useful anti-aircraft armament, turrets limit its heavy machine-guns too much for effective AA fire.