A tank is a track-laying, turreted, all-terrain AFV (armored fighting vehicle). They are distinguished from other AFVs primarily by purpose, armament, and mobility.
Key features of a tank:
- Self propelled mobile multipurpose gun
- Off road mobility through track based movement instead of wheel based
- All-around armor protection for tank crew and motor
During World War I, motorized vehicles were still relatively new and uncommon, but their use on the battlefield was imminent. The earliest motorized AFVs were tractors with metal plates bolted on to give some protection to the driver and passengers. The British Royal Navy developed the idea into the first tanks (called 'landships') by fully-enclosing the armored area, adding a tracklaying suspension, and guns mounted in turrets. Early tanks were large, had large crews, and moved about the same speed as marching infantry. They were 'male' or 'female', depending upon whether their armament was a large cannon or multiple smaller machine guns. The nickname 'tank' was a code-word used to confuse the enemy and maintain secrecy while they were being built and shipped to the front.
(more on WWI usage)
During World War II, the tank reached new heights of capability and sophistication. The German tanks, though technologically inferior to many of their opponents' tanks in the areas of armor and weaponry, were used most skillfully to achieve surprising strategic victories early in the war. The German doctrine stressed the use of combined-arms involving infantry and air support, and the tactic of the blitzkrieg (lightning warfare). Furthermore, the Germans were quick to supply their tanks with radios, which provided unmatched command/control.
It was true that nothing larger than machine guns could be mounted in any turret that this vehicle could carry. But with this disadvantage, it could be made ready for action by 1934 and it would at least serve as a training tank until our real combat tanks began to appear. [...] Nobody in 1932 could have guessed that one day we should have to go into action with this little training tank.
-- Heinz Guderian, Chief of German Army General Staff, on the Pz I.
(use of Pz I and Pz II training tanks due to lack of combat tanks)
The largest tank ever built was the Maus, designed in 1942 by Ferdinand Porsche under direct order from Adolph Hitler. Weighing 188 tons, the Maus was armed with a 128mm cannon and a coaxial 75mm gun, and covered with 180-240mm of armor. Only two prototypes were built, and both were lost while still undergoing testing. One of the Maus prototypes currently resides in the Museum of Armored Forces in Kubinka Russia.
(What's the true story behind the Maus in the museum? There are conflicting stories. In one version, both were scuttled at the factory prior to Soviet occupation, in another, one fought briefly before being captured.)
(T-34, tankettes, and other allied tanks of WWII; Patton, Rommel, Guderian, etc)
Since WWII, most of the changes in tank design have been refinements to targeting, ranging, and stabilization equipment, and to communications, and crew comfort. Armor has evolved to keep pace with improvements in weaponry, and guns have gotten bigger, but in most cases haven't fundamentally changed.
During the latter half of the 20th century, some tanks were armed with ATGMs (Anti-Tank Guided Missiles) which could be launched through the main gun barrel. In the U.S., the M60A2, M551 Sheridan, and prototype MBT-70, with 152mm barrel/launchers, used the Shillelagh infrared missile. The MBT-70 was canceled prior to production due to high cost, and superseded by the M1 Abrams, which used a conventional gun. Both the M551 and the M60A2 were widely considered failures; expensive, unreliable, and difficult to maintain. They were replaced by M60A3's (using conventional guns) and M2 Bradleys. ATGMs are currently mounted on lighter AFVs, such as the M901 ITV and the M2/M3 Bradley.
(HESH, HEAT, APDS/APFSDS, use of depleted uranium)
Sloping and curving armor both increase the effective thickness, as a projectile striking at an angle must cut through more armor than one impacting perpendicularly. They also increase the chances of deflecting projectiles.
Recent developments in tank armor have focused primarily on ways to defeat HEAT and other shaped-charge warheads.
Spaced armor is simply leaving hollow spaces in the armor to dissipate the energy of a shaped-charge warhead.
Composite (aka Chobham) armor was developed in the 1970s by the British and first used on the German Leopard II. It consists of layers of steel, ceramic, and plastic honeycomb, sometimes with layers of depleted uranium added. Composite is effective against both kinetic and shaped-charge munitions. Against kinetic penetrators, the brittle ceramic blunts the projectile while the softer steel layers absorb its kinetic energy. Still, it is significantly more effective against shaped charge munitions, so the depleted uranium layers are added to provide extra protection against kinetic penetrators.
Reactive armor, developed by Israel, uses layers of high explosive sandwiched between steel plates. When a shaped-charge warhead hits, the explosive detonates and pushes the steel plates into the warhead, disrupting the charge's plasma flow. It is not effective against kinetic penetrators.
(use of tanks and new tactics by Israelis in Arab-Israeli wars)
Tank also means:
- a shallow man-made pond or lake
- to decline or crash as in a stock declining rapidly in price
- a container used to store liquid or compressed gas
- an aquarium or terrarium
this article intentionally incomplete, more to come later, in the meantime feel free to edit/add to it