Tanks have come a long way since the 1940s. Here's a video that shows two British Army tanks: the World War II-era Churchill Mk. IV tank alongside the modern Challenger 2 tank.

The Churchill tank , first in service in 1941, was what was known as an "infantry tank"—heavily armed and armored, its job was to roll alongside the infantry, providing fire support against targets like machine gun nests, bunkers, and other threats foot soldiers couldn't handle themselves. At 24 feet long and 40 tons, the Churchill was considered one of the bigger tanks on both sides of World War II.

Infantry tanks were not necessarily expected to fight other tanks, and thus were slower and less heavily armed. Still, the Churchill was considered one of the better protected tanks of its time, with steel plate ranging from 102 to 16 millimeters.

Infantry tanks were also pretty slow; the Churchill's top speed was a mere 15 miles an hour, a mere 9.1 horsepower for every ton of tank. This particular Churchill was armed with a single 57-millimeter gun, but in wartime would have also been armed with two 7.92-millimeter machine guns.

More than seven thousand Churchill were built during World War II.

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The Challenger 2 tank, which came into service in 1998, is the standard main battle tank of the British Army. At 27 feet long and 65 tons, it's more than fifty percent heavier than its ancestor the Churchill. It speeds along at up to 37 miles an hour, more than twice as fast as the Churchill, and has more than double the horsepower to weight ratio.

Challenger 2 is armed with a 120-millimeter rifled anti-tank gun and, like the Churchill, it has two smaller 7.62-millimeter machine guns for engaging infantry, anti-tank missile crews, and light vehicles. Armored protection is classified but is known to use so-called "Chobham armor", a mixture of ceramic and metal composites also used in earlier versions of the M1 Abrams tank. The Challenger 2 in the video has an extra layer of reactive armor on the side of the turret and hull, and cage-like " slat armor " surrounding the rear engine compartment—two upgrades that came about as a result of experience in the Iraq War.

The difference between the two tanks in the video is huge. The Challenger is superior in every way, from speed to cross-country performance. And while everything seems to be twice as big, the performance gains are often exponentially better: the main gun of the Challenger may be twice as wide in diameter but's many, many times more effective. We've come a long way.

Update: this article was accidentally edited to imply that infantry tanks typically had less effective armor. The article has been corrected.

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