Another American casualty of the Soviet Union’s collapse: the M1 Abrams “Thumper” with a 140-mm gun and an automatic loading system

July 30, 2026

SaveSavedRemoved 0

Not long ago, I published an article discussing projects that were scrapped in the U.S. because the Soviet Union had collapsed and halted its development efforts. Among these projects was a new American main battle tank armed with a more powerful 140-mm gun. Since the USSR had halted such work, the U.S. did the same.

This article will describe the American tank project known as the M1 Abrams “Thumper,” which never went into mass production—perhaps for the best.

As you might guess, this vehicle was developed in the late 1980s. It was created in response to the need to significantly increase the firepower and armor penetration of the existing M1 Abrams tank, which was armed with a 120-mm gun.

A new 140-mm tank gun was developed for this purpose. The M1 “Thumper” prototype tank consisted of the hull of a production Abrams tank and a new turret, which was larger but had the same configuration, comfortably accommodating the new 140-mm gun and its crew, along with a rear-loading automatic loader. The project progressed to a running prototype, which underwent a series of tests to evaluate its performance and survivability on the battlefield.

Although the tests were generally successful, the “Thumper” project was ultimately shelved. The decision not to continue work on the project was influenced by several factors, primarily the high cost associated with developing and deploying the new tank. At that time, it was also decided that the existing 120-mm gun fully met current requirements and that establishing production of a new gun—and, more importantly, its ammunition—was unnecessary and excessively costly.

A Comparison of 140-mm and 120-mm Tank Shells

Interestingly, similar work was also underway in Germany on the Leopard 2, which they were also attempting to equip with a 140-mm gun. However, the cancellation of the American project put an end to the German one as well.

Unfortunately, no details about the project or how the tests were conducted have been posted online yet. All that is known is that the new American model was planned to be equipped with an automatic loader, which makes sense, since the weight of the ammunition had increased significantly and it had become difficult for the loader to handle it. A drawing of the American automatic loader—which, incidentally, is still not installed on their main battle tanks—has also survived; it consisted of two drums, each holding 17 rounds, for a total of 34 rounds per load.

Schematic of the automatic loader for the new Abrams tank

Actually, that’s all we know. We can only be glad that some bright minds decided to shut down the project after all; otherwise, by the time the Ukrainian crisis hit, these vehicles would have been fully operational long ago, and they would have caused us certain problems, even when firing from covered positions.