ISU-152 with the BL-10 experimental long 152mm
ISU-152 with the BL-10: The Soviet Super-Assault Gun That Could Have Been
At the twilight of World War II, as the Soviet Red Army surged ever-westward, its High Command was hungry for ever more destructive armored vehicles. The ISU-152, already infamous among the Wehrmacht as the “Zveroboy” (“Beast Slayer”) for its monstrous high-explosive firepower and broad utility against tanks, bunkers, and fortifications, became the centerpiece of several ambitious Soviet experiments. Of all the proposed upgrades, none promised to make a bigger bang—literally and metaphorically—than the fitting of the experimental BL-10 152mm gun.
But what was the BL-10, why was it developed, and what might have happened if it reached mass production? Let’s peer into this intriguing “what-if” of armored history.
Birth of a Beast: The ISU-152 Standard
The ISU-152 began life in 1943 as an assault gun and heavy tank destroyer, mounting a formidable ML-20S 152mm howitzer gun. With its combination of firepower, protection, and mobility, it was a weapon of both psychological and practical dominance. Its high-explosive shells could obliterate fortifications and snap the back of the fearsome Panther and Tiger tanks—if it landed a hit.
However, the ML-20S had limitations. Its muzzle velocity was relatively low (~600 meters per second), and accuracy at longer ranges was handicapped. Armor penetration, while impressive for its time, lagged behind emerging threats such as the German “King Tiger.”
BL-10: A New Hammer for the Red Army
Soviet engineers, ever eager to outdo German armor and rival Western designs, designed several experimental guns for the IS and ISU chassis. The BL-10 was one of the most ambitious—a 152mm gun that dwarfed the original ML-20S in terms of muzzle velocity and penetration.
Key statistics:
- Caliber: 152.4mm
- Barrel Length: 47 calibers (~7.17 meters; much longer than the ML-20S)
- Muzzle Velocity: Up to 1000 meters per second
- Penetration: Upwards of 200mm of armor at 2,000 meters
This performance potentially elevated the ISU-152 into a sniper-like tank destroyer capable of killing even late-war German heavies from standoff distances. By comparison, the standard ML-20S would struggle at such ranges or against such thick armor.
Prototype in Steel: ISU-152-1 and ISU-152-2
To test the new weapon, at least two prototypes were created on the ISU-152 chassis, sometimes referred to as ISU-152-1 (Object 246, BL-8 gun) and ISU-152-2 (Object 247, BL-10 gun), though names vary in sources. The defining feature was that exceedingly long barrel protruding from the ISU’s squat, armored casemate—a clear signal that something extraordinary lurked inside.
The BL-10 gun offered immense armor penetration, making the ISU-152 a rival to Germany’s own “super-tank destroyers” like the Jagdtiger. Its high-velocity shell and improved AP ammunition theoretically allowed defeat of almost any armor fielded during the war, including the Elefant, Tiger II, and even the Maus (in theory).
Challenges and Fate: Why the BL-10 Never Saw Battle
Despite dazzling test data, several factors doomed the ISU-152 with the BL-10 to the annals of experimental history:
- Technical Issues: The BL-10 experienced severe reliability and precision problems. Barrel wear was rapid. Some firing trials reported dangerous surges in breech pressure, elevating the risk to crews.
- Ergonomics: The huge length of the BL-10 made maneuvering within forests, ruins, and cityscapes problematic. It increased the vehicle’s silhouette and risked “barrel knocks” — striking the ground if the vehicle traversed ditches, thereby damaging the gun.
- Production Priorities: The war was ending, and the Red Army already possessed the combat-proven ISU-152 and its derivatives. Soviet planners shifted postwar towards larger-caliber, more modern designs (such as the ISU-130 and towed anti-tank artillery), or transitioned to new tank platforms entirely (like the IS-3 and T-10 heavy tanks).
- Overkill for the Postwar World: By 1945, the numbers of German super-heavies and bunkers had dwindled. What remained was more likely to be subdued by aircraft, conventional artillery, or the trusted (and easier-to-produce) standard ISU-152.
Legacy and Legend
No production ISU-152 with the BL-10 was ever deployed to the battlefield. Surviving photographs and test reports are all that remain, yet the prototype is a tantalizing glimpse at what might have been the ultimate Soviet tank destroyer of WWII. Had the ISU-152 BL-10 entered service in large numbers, it could have rewritten tactical doctrines on both sides—giving Soviet troops a weapon of unprecedented firepower, and potentially forcing desperate German adaptations.
Today, the legend of the ISU-152 with the BL-10 endures as a footnote in the great arms race of the Second World War: a symbol of Soviet ambition and willingness to push engineering to the limits. It stands alongside monsters like the German Maus, the American T29, and the British FV4005—a reminder that on the blackboard, and in the minds of engineers, no caliber was ever too big.
Further Reading & Museum Displays:
- Surviving ISU-152 BL-10 prototypes can occasionally be found in Russian museums, such as Kubinka.
- Technical archives offer more details, with blueprints and test reports sometimes surfacing in declassified collections.
- “The World’s Heaviest Tanks and Fighting Vehicles” by Michael Green provides overviews of the ISU experimental program.
Conclusion
The ISU-152 with the BL-10 was never more than a dream of steel and explosive ambition—but in that dream, we glimpse the arms race at its most feverish and inventive, a moment when the only limit was what could be loaded onto the shoulders of a Soviet assault gun.
