
The tank was invented by the British and French in 1916 to break the deadlock of trench warfare in World War I. The development of the machine gun, rapid-firing artillery, and smokeless powder made the World War I battlefield extremely lethal and after the initial German successes in Belgium and northern France, settled into a stalemate. Early efforts at overcoming this firepower involved the initial thoughts of the “spirit of the offense” overcoming all obstacles which led to high casualties and didn’t work, to the “artillery destroys, infantry occupies” strategy of the Allies with millions of artillery rounds being expended in week-long bombardments – which only drove the defenders further underground until the bombardment stopped and then they’d come up and still inflict heavy casualties. The Germans tried using gas warfare to break through the trenches, but that didn’t work and the Allies employed their own chemical munitions. Airpower was in its infancy and didn’t have a decisive effect on the ground. Eventually, the Allies developed tanks as a mobile, armored machine gun platform that could cross “no man’s land” and break through the enemy obstacles.
Although the tank has come to be associated with the German panzers and “blitzkrieg” of World War II, the Germans actually fielded a paltry twenty tanks in World War I, compared to over 5,000 Allied tanks. The Germans instead looked for a doctrinal solution to trench warfare, developing their infiltration tactics which emphasized small unit initiative and a flexible battle plan to channel all available forces to the path of least resistance. The German solution almost worked and led to significant gains in 1918 (significant compared to the rest of World War I on the Western Front) but they took heavy casualties and that ultimately broke the back of the German army. It wasn’t until they matched the concept of infiltration tactics with improved technology of tanks, radios, and aircraft that they developed what many people call “blitzkrieg” in World War II (which led them to victory from 1939-1941, despite in many cases the Allies having tanks with heavier armor, armament, or superior numbers).
A British Mk IV heavy tank, employed during World War I.
The British tanks of World War I were all “heavy” tanks – large, turretless tanks with tracks going around the entire hull (giving them the ability to climb high vertical obstacles and trenchlines). They were developed in the “male” and “female” variety, the “male” tanks mounting cannon in the sponsons for destroying enemy fortifications while the “female” version had numerous machine guns for anti-infantry work. The French on the other hand developed “light” tanks with a fully rotating turret. Both types of tanks moved at about the same speed – not much faster than a person could walk – they also frequently broke down, had thin armor, and unpleasant crew conditions (imagine a dozen people in a pitching enclosed box with a loud engine in there with you, shellfire all around, and with signal flags, a few vision ports, and carrier pigeons your only link to the outside world).
Despite the initial shock of their appearance, the Germans quickly developed anti-tank tactics (employing “elephant guns” and artillery pieces in the direct fire role) and it was nearly a year until the first really successful tank attack took place at Cambrai in late 1917. The difference at Cambrai was the employment of tanks in mass (versus “penny packets” in earlier attacks) and avoiding the week-long artillery bombardment that churned up the ground making it difficult to traverse and alerted the enemy and his reserves to be ready for an attack.

The German StuG assault gun, employed 1940-45. Initially developed as a cheaper version of the tank for infantry support, this assault gun is a little over 6ft high giving it a very low silhouette and thick frontal armor. This comes at the cost of a rotating turret, which particularly hurts if the vehicle is immobilized.
During the Inter-War period, the Germans weren’t allowed to develop tanks and due to budget cuts the Allies didn’t make significant improvements on their designs. There was talk of motorization of the previously foot-bound infantry, or mechanizing the horse-mounted cavalry, with the British being major proponents of that. However, tight budgets and an entrenched, traditional establishment delayed these reforms in any amount until the eve of World War II. Despite their rushed re-armament starting in 1933, the German tanks at the start of the war were still fairly primitive with their main advantage being in communication (radios in all tanks versus just the “command” tanks). Then the Germans got a rude shock in 1941 when they started encountering the new Soviet T-34 tanks and the heavy KV-1 tanks, both of which had sufficient armor to defeat the standard German tank-mounted cannon and all but the heaviest anti-tank guns. That in turn spurred the Germans on to developing their Tiger and Panther tanks and up-gunning their other tanks to fight the Soviets. The Allies were slow in catching up and it wasn’t until late 1944 and 1945 that the Allies had tanks which might be capable of matching the German best in a fair fight. Of course, warfare isn’t supposed to be fair and the massive Allied superiority in artillery, air power, and sheer weight of numbers meant that German tank superiority in one-on-one engagements didn’t pan out to much in the big picture.

Tank cannon in World War II. The Tiger I tank had an 88mm gun, whereas the Sherman had a 75mm. No big deal, right? It’s a measly 13mm – half an inch of difference. However, gun diameter is only one part of the equation: muzzle velocity is the other. Starting in 1942, the Germans began to use long-barreled guns (longer barrel = higher muzzle velocity and greater accuracy), giving the Tiger 88 (top-most cannon) the ability to cut clean through a Sherman tank, and the Sherman 75 (third from the top) the ability to kill a Tiger at close range from the rear.
Post-war, tanks moved from the 70-ton monstrosities that the Germans built to more manageable all-around “main battle tanks” in the 40-50 ton range. The main improvements were matching mobility with heavy armor and firepower, as well as developing fire control computers, laser rangefinders, and night vision capabilities. The widespread employment of shaped charges in the post-war period and their high level of effectiveness led to the French and Germans developing lightly armored, highly mobile vehicles with the thought process that if you get hit anyways you’re going to be in trouble. The British and Americans opted for the heavier tanks, sacrificing mobility for better protection. It wasn’t until the development of composite armor in the late 1970s that armor once again got the upper hand over ammunition, leading to the modern-day M1 Abrams tank, the British Challenger, and the German Leopard 2 (and the weight moved back up to the 60-70 ton range).

The British Chieftan heavy tank of the 1970s – its rifled 120mm cannon was the most powerful gun in the West until the widespread adoption of the German 120mm smoothbore in the mid-80s.
In contrast to Western practices, the Soviets kept their tanks in the 40-50 ton range even through the present day. Their tanks generally had a smaller silhouette than Western types, possible by sacrificing how much the gun can elevate or depress, and also by limiting the size of their tankers and sacrificing crew comfort. Starting in the 1980s, they were also slow to adopt thermal night-vision technology for their tanks and due to size and weight restrictions didn’t store the ammunition separate from the crew (in contrast, modern Western tanks store ammunition in blow-out compartments designed to save the crew in the event of an ammunition explosion). In an interesting twist to World War II, the victorious Allies adopted the German “quality over quantity” approach in developing heavy main battle tanks while the victorious Soviets went the other way, deploying tens of thousands of not-quite-as-good medium tanks in Eastern Europe.
The Russian T-72 main battle tank. Note the snorkel in the turret roof, which gives Russian tanks the ability to ford rivers and streams given suitable riverbed conditions and assuming the engine doesn’t stall while you’re underwater.
Today, the main growth in technology for tanks is in command and control equipment (digital maps, remote sensors to give a buttoned-up crew better visibility, etc.) and active protection systems (designed to shoot down or destroy incoming projectiles instead of relying on passive armor to absorb it).