Why the 17 Pounder 76mm Gun on the Sherman Firefly Outperformed Other 75mm Guns

During World War II, the choice of tank guns had a significant impact on combat effectiveness. One of the standout guns was the 17 Pounder (17 pdr) 76mm gun on the Sherman Firefly, which was notably superior in armor penetration compared to other 75mm guns used in the war. In this article, we delve into the reasons behind its success and explore how velocity and ammunition design played pivotal roles.

The 17 Pounder 76mm vs. 75mm Guns

The 17 pdr 76mm gun, officially designated as the Ordnance QF 17 pounder, was a British tank gun developed during the war. Its specification as a 76mm gun was different from the 75mm designations of other guns. Contrary to popular belief, the 17 pdr was actually a 76mm equivalent, and the extra millimeter in the specification made a notable difference in performance.

Velocity and Penetration

One of the key factors in the superior performance of the 17 pdr was its high muzzle velocity. The 17 pdr fired its shells at a velocity that was 50% faster than the 75mm rounds. This significantly enhanced its penetration capabilities, which is crucial in tank combat.

Penetration in tank guns is directly correlated with velocity. This means that while the diameter of the gun might be similar, the difference in cannon velocity can lead to vastly different performance in terms of armor penetration. The 75mm guns used by various nations, including the US and Germany, were primarily designed for infantry support rather than anti-armor capabilities. Their HE (High Explosive) rounds were designed to be lighter and thinner, allowing them to carry a larger payload of explosives. This meant that while the 75mm round had excellent HE capabilities, it lacked the penetration power of the 17 pdr.

Ammunition Design

The 17 pdr gun required a different approach to ammunition design. Unlike the 75mm guns, it had no high-explosive (HE) round. Instead, the 17 pdr primarily used AP (Armor-Piercing) rounds with a discarding sabot. The sabot helped the shell to maintain its integrity and improve its accuracy at longer ranges. However, it also made the 17 pdr less effective against soft targets as the discarding sabot round was highly inaccurate unless fired at very close range.

A comparable 76mm gun, such as the German 75mm anti-tank gun, showed that a 76mm diameter gun could perform comparably to the 17 pdr. When both guns were tested side by side, the difference in capabilities was minimal unless the 17 pdr used its discarding sabot round. However, this round was so inaccurate that it was difficult to effectively target distant or well-protected targets.

Practical Applications in Combat

During World War II, the 17 pdr was deployed as part of the Sherman Firefly tank. Given that most targets faced by Allied forces were soft targets such as infantry, trucks, artillery, and anti-tank guns, the Sherman Firefly was often equipped with the 17 pdr to handle more heavily armored enemy targets like German Panzers. The high-velocity penetrative capabilities of the 17 pdr were utilized against tough targets, while the 75mm Shermans covered soft targets.

US Army experience with the 17 pdr was not as positive. The US completely rejected the 17 pdr in the M4 Sherman because of its poor ergonomic design. Rebounding sand, dust, and debris made it difficult to spot where the shells were falling. Accuracy issues meant that the 17 pdr was not particularly useful for hitting soft targets. This led to the Sherman continuing to use various 75mm guns, as these were more effective for their primary role of supporting infantry.

Conclusion

The 17 pdr 76mm gun on the Sherman Firefly outperformed other 75mm guns used in World War II, primarily due to its superior velocity and the design of its ammunition. While the 75mm rounds were excellent for their HE role, the difference in velocity between the two meant that the 17 pdr could penetrate armor more effectively. This was particularly true when using the discarding sabot round, which, despite its inaccuracy, provided the necessary penetration against heavily armored targets.

Understanding these differences in gun performance can help modern enthusiasts and historians appreciate the strategic decisions made by different nations during the war. The choice of ammunition and the focus on velocity are crucial elements that determined the success of one tank gun over another in World War II.