The legendary M1 Abrams tank has been on the testing ranges and battlefields for 40 years, saving dozens or even hundreds of crews who were able to unleash hellish fury on their enemies while surviving dozens of blows from enemy tanks' main guns.

It's all thanks to American and British engineering that has stood the test of time.

An MBT-70 fires an anti-tank missile in testing. (Mark Holloway, CC BY 2.0) That's right, British engineering was a key ingredient in creating this dominant war machine. The need for the M1 program came about because of the failure of the MBT-70 program, a joint U.S.-German program to develop a replacement for the M-60 Patton, a capable but aging tank that wouldn't be able to hold the line against Soviet armor forever. The MBT-70 would have had a low profile, good armor, and a massive 152mm main gun that could fire anti-tank missiles. It was fast, hitting 43 mph in testing, which would've made it the fastest tank in the world at the time. And it had a weird feature where the driver's seat was located in the turret but automatically rotated to always face the direction of travel.

An MBT-70 prototype at the United States Army Ordnance Museum at Aberdeen Proving Ground, Maryland. (Mark Pellegrini, CC BY-SA 2.5) But for all its bells and whistles, the MBT-70 had a lot of problems. It was too heavy to use most of the armored infrastructure then available in Europe, including recovery vehicles and bridges. It cost more than originally planned, too. But worst of all, its caseless ammo had a tendency to swell, making it unusable in combat and potentially even starting fires inside the vehicle. The project was ultimately canceled due to costs, but some of the technical specs and designs were carried over into the XM1 project, which would churn out its first M1 Abrams in 1978. The M1 shared the low-profile of the MBT-70 as well as blowout compartments for ammunition and a shallow turret.

An M1 Abrams taking part in Getica Saber 17. (U.S. Army Spc. Kelsey M VanFleet) The Abrams was even faster than its speedy predecessor. On paper, it was slated to peak at 45mph, but in capable tankers' hands, it was a little faster. Originally, its gun was shrunk down to 105mm, but later models were upgraded to 120mm — still a far cry from the 152mm of the MBT-70. But with sabot rounds controversially made from depleted uranium, it still had enough power to punch through nearly anything. Even modern explosive reactive armor has trouble with sabot. But the the most revolutionary upgrades that the Abrams brought to the table are in the armor and engines. The armor is Chobham armor that Britain quietly revealed to the U.S. while it was developing the Abrams. It is, essentially, a layered sandwich of reactive plates encased in metal with elastic layers underneath. It provides great protection against high-explosive rounds, kinetic energy penetrators, and armor-piercing rounds. The initial Abrams was so popular with tankers that they gave rave reviews in 1982 to a visiting writer and bragged that the tank would "remain contemporary" for at least 10 years. 30 years after that article was published, the notion seems cute.

An M1 Abrams tank fires in Strong Europe Tank Challenge 2018. (U.S. Army Christoph Koppers) But the Abrams hasn't survived for so long because it was awesome rolling off the line. The tank has been upgraded every few years since its debut. It has received not only a new gun, but improved optics and a better powertrain. And those are just the upgrades implemented before the 1990 Gulf War. Since then, everything from the ammo to the armor to the electronics have been upgraded. It can power its computers without running the high-consumption turbines, its formerly vulnerable gas tanks are now better protected and it has defenses against IEDs and large anti-tank mines. It has even gotten reactive armor with the TUSK — the Tank Urban Survival Kit. This is basically a bunch of bombs strapped to the outside of the tank that deflect enemy blasts and penetrators.