Tank

A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility and tactical offensive and defensive capabilities. Firepower is normally provided by a large-calibre main gun in a rotating turret and secondary machine guns, while heavy armour and all-terrain mobility provide protection for the tank and its crew, allowing it to perform all primary tasks of the armoured troops on the battlefield.
Tanks were developed and first used in combat by the British during World War I as a means to break the deadlock of trench warfare. They were first deployed at the Battle of Somme in limited numbers. During construction, to conceal their true identity as weapons, they were designated as water carriers for the Mesopotamian campaign and referred to as "tanks" (as in "water tank"). However, there are two other proposed etymologies – these are discussed in the Etymology section below.
Interwar developments in both design and tactics evolved during World War II, producing important concepts of armoured warfare which persist to this day and were prominently displayed during World War II. The Soviet Union introduced the T-34, one of the best tanks in service throughout the war. Germany introduced blitzkrieg, a strategy which makes use of massed concentrations of tanks supported by artillery and air power to break through the enemy front and cause a complete collapse in enemy resistance.
Tanks in the Cold War advanced to counter greater battlefield threats. Tanks became larger and their armour became thicker and much more effective. Advances in manufacturing late in the war allowed the mass production of composite armor. Aspects of gun technology changed significantly as well, with advances in shell design.
Today, main battle tanks are considered a key component of modern armies. Modern tanks seldom operate alone, as they are organized into armoured units which involve the support of infantry, who may accompany the tanks in infantry fighting vehicles. They are also usually supported by reconnaissance or ground-attack aircraft. However, the prevalence of unconventional and asymmetric warfare have led to some questioning the utility of the traditional armoured force.

Chemical Weapon

Chemical warfare (CW) involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from Nuclear warfare and Biological warfare, which together are the three tenets of NBC, the military acronym for Nuclear, Biological, and Chemical (warfare or weapons). Neither of these falls under the term conventional weapons which are primarily effective due to their destructive potential. Chemical warfare does not depend upon explosive force to achieve an objective. Rather it depends upon the unique properties of the chemical agent weaponized. A lethal agent is designed to injure or incapacitate the enemy, or deny unhindered use of a particular area of terrain. Defoliants are used to quickly kill vegetation and deny its use for cover and concealment. It can also be used against agriculture and livestock to promote hunger and starvation. With proper protective equipment, training, and decontamination measures, the primary effects of chemical weapons can be overcome. Many nations possess vast stockpiles of weaponized agents in preparation for wartime use. The threat and the perceived threat have become strategic tools in planning both measures, and counter–measures.

Biological Weapon

Biological warfare (BW), also known as germ warfare, is the deliberate use of disease-causing biological agents such as protozoa, fungi, bacteria, protists, or viruses, to kill or incapacitate humans, other animals or plants. Biological weapons (often referred to as bioweapons) are living organisms or replicating entities (virus) that reproduce or replicate within their host victims.

Biological weapons may be employed in various ways to gain a strategic or tactical advantage over an adversary, either by threat or by actual deployment. Like some of the chemical weapons, biological weapons may also be useful as area denial weapons. These agents may be lethal or non-lethal, and may be targeted against a single individual, a group of people, or even an entire population. They may be developed, acquired, stockpiled or deployed by nation states or by non-national groups. In the latter case, or if a nation-state uses it clandestinely, it may also be considered bioterrorism.

There is an overlap between biological warfare and chemical warfare, as the use of toxins produced by living organisms is considered under the provisions of both the Biological Weapons Convention and the Chemical Weapons Convention. Toxins and Psychochemical weapons are often referred to as midspectrum agents. Unlike bioweapons, these midspectrum agents do not reproduce in their host and are typically characterized by shorter incubation periods.