The Evolution of M1 Abrams: From 105 mm to 120 mm Main Armament

The Abrams Main Battle Tank (MBT) series, particularly the M1 Abrams, has seen significant changes in its primary armament throughout its evolution. This article delves into the specific case of the change from the 105 mm cannon to the more powerful 120 mm cannon, examining the context, technical details, and reasons behind these modifications.

Background: The 105 mm Cannon

Originally, the M1 Abrams was equipped with a 105 mm M68 tank gun. This choice was made in the 1970s when the primary threat was the Soviet T-62 and T-72 tanks. While effective against these targets, the 105 mm cannon faced limitations as the military began to anticipate more advanced Soviet tank designs in the post-Vietnam era. By the 1980s, it became clear that the 105 mm cannon was no longer sufficient to penetrate advanced Soviet tanks like the T-80U and T-72B, which were armed with advanced composite armor.

The Challenges: Soviet Tanks and the 140 mm ATAC

The increasing capabilities of Soviet tanks posed significant challenges for the US military. Notably, the T-80U and T-72B, equipped with advanced armor technologies such as the Kontakt-1/5 reactive armor, were particularly difficult to defeat. The M833 APFSDS (Armor-Piercing, Fin-Stabilized, Disc-Shaped, Center-of-Gravity) round, which was the primary ammunition used by the US Army, found itself ineffective against these tanks due to their advanced armor and soft/hard kill systems.

Addressing the Threat: The ATAC and Its Limitations

In response to these challenges, multiple nations embarked on projects to develop new guns and ammunition. The Germans, French, and Soviets themselves explored options such as the ATAC (Advanced Tandem Armor Cratering), a 140 mm cannon concept. While the ATAC showed promising results in laboratory and limited testing, its development was ultimately deemed insufficient. The project's dissolution due to various technical and logistical issues made it clear that a new approach was necessary.

The 120 mm Cannon: A Feasible Solution

Following the failure of the ATAC project, the US military returned to the CATTB (Continuous Ammunition Tank Technology Base) program. The mantlet used in the ATAC was adaptable, capable of accommodating a 120 mm Rh-120 cannon. The 120 mm cannon, with its higher performance and improved armor-piercing capabilities, was chosen to upgrade the M1 Abrams. The 120 mm L/44 cannon was modified significantly for enhanced performance, ensuring that it could meet the needs of an evolving battlefield.

Performance and Penetration

The 120 mm cannon offers substantial improvements in terms of penetration and overall effectiveness. The improved 120 mm ammunition, combined with the L/44 barrel, allows the M1 Abrams to engage and destroy heavily armored Soviet tanks. In this context, the 120 mm cannon delivered a significant upgrade from the 105 mm cannon, enabling the M1 Abrams to remain a potent threat in the face of advanced armor technology.

Conclusion: The Iterative Nature of Military Modernization

The transition from the 105 mm cannon to the 120 mm cannon in the M1 Abrams exemplifies the iterative nature of military modernization in response to evolving threats. From the initial 105 mm L/44 to the 120 mm L/44, the M1 Abrams has continually adapted to meet the demands of a changing battlefield. This article highlights the challenges faced by the US military in the 1980s and early 1990s, culminating in the adoption of the 120 mm cannon as a pivotal upgrade to the M1 Abrams series.