T-54s, T-55s, Type 59s or Type 69s at Diwaniyah, Iraq

The jack-in-the-box effect is a specific effect of a

catastrophic kill A catastrophic kill, K-Kill or complete kill is damage inflicted on an armored vehicle that renders it permanently non-functional (most commonly via fire and/or an explosion). Among tank crewmen it is also commonly known as a ''brew up'', coine ...

on a tank or other turreted armored vehicle in which an

ammunition Ammunition (informally ammo) is the material fired, scattered, dropped, or detonated from any weapon or weapon system. Ammunition is both expendable weapons (e.g., bombs, missiles, grenades, land mines) and the component parts of other weap ...

explosion An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...

causes the tank's turret to be violently blown off the chassis and into the air. It is named after the child's toy, the

jack-in-the-box A jack-in-the-box is a children's toy that outwardly consists of a box with a crank. When the crank is turned, a music box mechanism in the toy plays a melody. After the crank has been turned a sufficient number of times (such as at the end of ...

, in which a puppet pops up. Most of the time the crew inside does not survive.

Mechanics

If an

anti-tank Anti-tank warfare originated from the need to develop technology and tactics to destroy tanks during World War I. Since the Triple Entente deployed the first tanks in 1916, the German Empire developed the first anti-tank weapons. The first de ...

projectile or

shaped-charge A shaped charge is an explosive charge shaped to form an explosively formed penetrator (EFP) to focus the effect of the explosive's energy. Different types of shaped charges are used for various purposes such as cutting and forming metal, init ...

blast Blast or The Blast may refer to: *Explosion, a rapid increase in volume and release of energy in an extreme manner *Detonation, an exothermic front accelerating through a medium that eventually drives a shock front Film * ''Blast'' (1997 film), ...

manages to penetrate a turreted

armored vehicle Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, shells, rockets, and missiles, protecting the personnel inside from enemy fire. Such vehicles include armoured fighti ...

's hull and subsequently its

storage area, the

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

and

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and ...

can be sufficient to cause

cooking off Cooking off (or thermally induced firing) is unfired weapon ammunition exploding prematurely due to heat in the surrounding environment. The term is used both for detonation of ammunition not loaded into a weapon, and unintended firing of a loa ...

sympathetic detonation A sympathetic detonation (SD, or SYDET), also called flash over or secondary/secondaries (explosion), is a detonation, usually unintended, of an explosive charge by a nearby explosion. Definition A sympathetic detonation is caused by a shock wav ...

of some or all of the tank's unfired

explosive shell A shell, in a military context, is a projectile whose payload contains an explosive, incendiary, or other chemical filling. Originally it was called a bombshell, but "shell" has come to be unambiguous in a military context. Modern usage ...

s and

propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the e ...

. This causes a massive and instantaneous

overpressure Overpressure (or blast overpressure) is the pressure caused by a shock wave over and above normal atmospheric pressure. The shock wave may be caused by sonic boom or by explosion, and the resulting overpressure receives particular attention when m ...

in the sealed internal compartment of the tank, until it explodes outwards through the weakest point in the otherwise homogeneous compartment, namely the turret ring, blowing the turret completely off the chassis and into the air in a gush of

flame A flame (from Latin '' flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density they ...

. The jack-in-the-box effect is known to occur in tanks which are "buttoned up" (i.e. with all hatches closed and locked), and which have internally stored ammunition and no blow-off panels on the ammunition storage area. Tanks of the World War II era were frequently seen to have lost their turrets in this manner, largely owing to the design of that era, as at the time it wasn't recognized that there was a need for special shielding of the tank's ammunition storage compartments. Some modern tanks such as the Russian

T-72 The T-72 is a family of Soviet/ Russian main battle tanks that entered production in 1969. The T-72 was a development of the T-64, which was troubled by high costs and its reliance on immature developmental technology. About 25,000 T-72 tanks h ...

T-80 The T-80 is a main battle tank (MBT) that was designed and manufactured in the former Soviet Union and manufactured in Russia. The T-80 is based on the T-64, while incorporating features from the later T-72. The chief designer of the T-80 was ...

, and

T-90 The T-90 is a third-generation Russian main battle tank. It uses a 125mm 2A46 smoothbore main gun, the 1A45T fire-control system, an upgraded engine, and gunner's thermal sight. Standard protective measures include a blend of steel and compo ...

, feature a compact three-crew design with an auto-loading mechanism, eliminated the need for a fourth crew member who is the loader. While this gives the tank a lower profile so it can better ''avoid getting hit'' by enemy tanks, the tradeoff is being extremely vulnerable ''once hit'' (even an indirect hit) which will likely set off the ammunition stored in a ring along the inside of the turret right next to the crew. The newest Russian tanks are still susceptible to this effect, even with

composite armour Composite armour is a type of vehicle armour consisting of layers of different material such as metals, plastics, ceramics or air. Most composite armours are lighter than their all-metal equivalent, but instead occupy a larger volume for the s ...

and

Reactive armour Reactive armour is a type of vehicle armour that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. It is most effective in protecting against shaped charges and specially hardened kinetic ener ...

, as they retain the compact three-crew cabin. Many modern Western tanks (for instance, the

M1 Abrams The M1 Abrams is a List of main battle tanks by generation, third-generation American main battle tank designed by Chrysler Defense (now General Dynamics Land Systems) and named for General Creighton Abrams. Conceived for modern Armoured warfa ...

Leopard 2 The Leopard 2 is a 3rd generation main battle tank originally developed by Krauss-Maffei in the 1970s for the West German army. The tank first entered service in 1979 and succeeded the earlier Leopard 1 as the main battle tank of the West Germ ...

and Leclerc series, to name a few) feature ammunition compartments designed to fail safely under fire as a

firepower kill Firepower is the military capability to direct force at an enemy. (It is not to be confused with the concept of rate of fire, which describes the cycling of the firing mechanism in a weapon system.) Firepower involves the whole range of potent ...

– when damaged, vents open to channel ignited

s and

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...

s away from the crew cabin. These tanks have a loader as the fourth crew member, where training doctrine mandates that the ammunition compartment door must be closed before loading the main gun, so that there is only one shell likely to be exposed in the turret at any time which limits the risk to the crew. Whether an enemy hit ruptures the ammunition compartment or penetrates the tank's interior, the crew have a higher chance of survival so they can return the tank to a maintenance center or at least escape their disabled vehicle.

References

Bibliography

*''The Eve of Destruction: The Untold Story of the Yom Kippur War'', Howard Blum, Harper Perennial, 2004 *''Tanks of World War II''; Jane's Information Group, HarperResource, 1995 *''Jane's Tank Recognition Guide'', Christopher F. Foss and Jane's Information Group, Harper-Collins Publishers, 2003 {{Refend Military slang and jargon Armoured warfare