Armor first appeared on the battlefield thousands of years ago, typically using layers of leather, wood – even silk – to deflect, slow or stop arrows and spears. As offensive weapons advanced, from Greek fire and boulder-launching trebuchets to the English longbow and Mongol composite bow to early firearms, armor-makers had to advance their defensive craft to counter it.

The Greeks and Romans used armor on their chariots and siege weapons. Leonardo da Vinci designed what may have been the first mobile armored tank – a cone-shaped war wagon with a full 360-degree complement of cannon. It was never used by his 15^th century patrons, but a working model recently was built, using materials available to da Vinci and following his precise instructions, demonstrating it was more than a flight of imagination.

The heavy Tiger would have been more evenly matched against the American M26 Pershing, but the U.S. had slowed production of its heavy tanks in order to mass produce the more agile Sherman and tank destroyers such as the M10, M36, and the M18 Hellcat.

The first serious use of tanks came during World War I, but the vehicles were cumbersome, limited in battlefield mobility and often more dangerous than protective to their crews. By World War II, however, tank technology had advanced at a level similar to the evolution of military aircraft between the two wars. Nazi Germany held the technological advantage, but the British, Russians, Japanese and Americans were not far behind.

German Field Marshall Erwin Rommel, U.S. Gen. George S. Patton and British Field Marshal Bernard Montgomery earned permanent places in military history for their World War II use of massive tank forces – not only in tank-on-tank encounters, but to overrun infantry, crush enemy defenses and capture cities. Rommel’s Afrika Korps and other commands were predominantly equipped with comparatively light Panzers; Patton’s Third Army with medium-weight M4 Shermans; and Montgomery’s Eighth Army with the well-armored but underarmed Matilda, a series of “cruiser” tanks, and U.S.-built medium M3 Grants/Lees and Shermans.

Germany also fielded the heaviest tank to that point – the Tiger – primarily as a counter to the unexpectedly formidable Soviet T-34 and KV-1 tanks the Nazis encountered during Operation Barbarossa, the June 1941 invasion of their former ally, the Soviet Union. The heavy Tiger would have been more evenly matched against the American M26 Pershing, but the U.S. had slowed production of its heavy tanks in order to mass produce the more agile Sherman and tank destroyers such as the M10, M36, and the M18 Hellcat.

And when the Cold War turned hot in Korea, the United States found itself facing the same kind of Soviet-built heavy armor that had led the Germans to introduce the massive Tiger a few years earlier.

“Once the Cold War began, the U.S. believed there was a ‘tank gap’ – looking at the heavily mechanized status of the Warsaw Pact, we found the Soviets had far more and better tanks than we could field in the late 1940s and early ‘50s,” noted Dr. Robert S. Cameron, Armor Branch historian at the Army Armor Center at Fort Benning, Ga.

 

And when the Cold War turned hot in Korea, the United States found itself facing the same kind of Soviet-built heavy armor that had led the Germans to introduce the massive Tiger a few years earlier.

“When the Korean War broke out, the direction of armor issue became critical. The U.S. did not see Korea as an isolated regional conflict; our concept then was that the Kremlin was at the center of all global Communist efforts,” Cameron said. “So war breaking out on the Korean peninsula was seen as a potential prelude to the outbreak of World War III, with a center point in Central Europe. And the U.S. was not ready to wage a major tank war in Central Europe – or Asia.”

A 1949 government advisory panel on armor found the U.S. Army not only had no tanks in production, but none in development capable of defeating the Soviet platforms, which the USSR had provided to its allies around the globe. Calling the situation critical, the panel warned the United States had to immediately ramp up both development and production of new tanks or face the possibility of spending the first two and one-half years of any major future war without enough tanks to support its ground forces.

“We went into conflict with the North Koreans with the same tank mix we had at the end of World War II,” Cameron continued. “The enemy invasion of the south was spearheaded by a mix of Soviet-built tanks – primarily the T34/85 – and infantry. The M24 Chaffee light tank was the basic tank the U.S. had in Korea – and it was not intended for tank-to-tank fighting. In the course of that first year, there was a focused effort to get more and heavier tanks into Korea – Shermans and Pershings. Gradually, the balance began to swing in favor of the U.S. and its UN allies.”

Realizing it would be difficult to match the Soviet threat tank-for-tank, the U.S. turned to the technological multiplier in the mid-1950s.

Because the United States saw Korea as a microcosm of what could happen in Europe, the government scrambled to overcome the perceived “tank gap” that heavily favored the USSR and Warsaw Pact.

Much military strategy at the time incorporated a series of equations developed by English mathematician and engineer Frederick Lanchester at the height of World War I regarding the power relationships between opposing forces. Lanchester’s Square Law for long-range modern combat contended that, all other factors being equal, the power of a single combat unit relative to the combat power of an enemy of a given size is the square of the number of members of that unit; that is:

One tank has the combat power of one tank – 1² = 1

Two tanks have four times the relative combat power of a single tank – 2² = 4

Lanchester’s formula did not apply to technological force, however, only numerical. Thus it could take up to five Sherman tanks to knock out a single German Tiger. Realizing it would be difficult to match the Soviet threat tank-for-tank, the U.S. turned to the technological multiplier in the mid-1950s.

In Korea, the North’s tank force had been nearly destroyed by 1950 and America’s growing – and increasingly heavy – armor took on the role of infantry support, casualty evacuation and even logistics carrier. In heavier, often spread out, fighting against the Chinese, they were used as strong points around which infantry could rally if in danger of being overrun.

“It was quite a different employment of armor than what folks had thought of coming out of World War II,” Cameron said. “There also was an accelerated pace to get new tanks into the field, not just because of Korea, but due to a fear of an outbreak of conflict in Central Europe. So the M48 Patton underwent a rapid development and fielding pace, going from raw engineering concept to fielding in less than three years. It never saw service in Korea, but was shipped straight to Central Europe.

“Coming out of World War II and into Korea, the Army thought it needed three types of tanks – light, medium and heavy. At the end of World War II, the M24 was considered medium, but during Korea was reclassified as light. The problem for light tank design – indeed, all light armor – is if you want a light armor system capable of taking on enemy armor with upgraded ballistic protection, you need a bigger gun, which translates into a heavier vehicle. But it’s also nice to have something stealthier and more mobile. Throughout the Cold War, the Soviets kept upgrading their armor and armament and light tanks had a hard time keeping up.”

Korea also saw the introduction of a new light tank – the M41 Walker Bulldog – as a replacement for the M24. By the end of the Korean War, the U.S. had a large number of M48s in the field, along with the M41 and the M103 Heavy Tank – a variant of the M48 with a six-man crew, 120mm gun and two-piece cartridge that was the heaviest and most heavily armed U.S. tank until development of the M1A1 Abrams in the mid-1980s.

“These were to be grouped into heavy tank battalions to counter a major Soviet tank assault. It was similar to how the Germans used Tigers in WWII, but as we went through the 1950s, not many 103s were built (most were turned over to the Marines),” Cameron said. “But for the Army, the nature of the threat that led to the Heavy Tank design was found to be overrated. There had been exaggerated concepts of what Soviet tanks could do and, as people took a more realistic look at Soviet capabilities, the need for a heavy tank diminished. And the M48 became more versatile as the main battle tank (MBT) concept emerged.

“There also was a new look at the trend to light tanks. The M5 [Stuart, the Army’s standard light tank at the beginning of World War II], then the M24, then the M41 – the trend was the same as any other tank: Increasing gun caliber, heavier weight, heavier armament, heavier armor. As you moved through the 1950s, then, the Army began looking at a single platform instead of the light-medium-heavy triad.”

Perhaps the single biggest change in tank structure was how armor was incorporated.

“The big advance came in the change from a cast hull, which had its own problems because, when hit, even if you did not penetrate, the back side of the hull would splinter off and throw fragments into the interior,” according to Dr. Douglas Templeton, deputy associate director for ballistic protection at the Army’s Tank Automotive Research, Development & Engineering Center (TARDEC). “The M60 still used cast iron. The big change came in what evolved into the Abrams, with welded armor plate instead of cast.

“In addition, we moved into using aluminum as the availability became greater. Probably the world’s best armored vehicle is the U.S. M113 armored personnel carrier, introduced in the 1960s but still seen around the world. It’s an all-aluminum vehicle, basically a box on tracks, not as heavily armored as a tank, but still well-protected and extremely versatile.”

Editor’s note: This article was first printed in The Year in Defense: Review Edition in an abridged version as “Armor: Three Decades of Advances.” It is now appearing online in its original form, in four parts. This article first appeared online on November 10, 2014