H

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H

Halogen

Any of the five chemical elements in group VIIa of the Periodic Table. Fluorine, Chlorine, Bromine, Iodine, and the radioactive Astatine are nonmetallic, monovalent negative ions and exist in pure form as diatomic molecules. The first four elements exhibit an almost perfect gradation of physical properties. Fluorine is the least dense and chemically the most active, displacing other halogens from their compounds and oxygen from water. Iodine is the least active. The halogens form numerous compounds with each other, and with other elements, such as hydrogen halides, metal halides (Salts), and halocarbons.

Hangfire

The detonation of an explosive charge at some nondetermined time after its normally designed firing time.

Temporary failure or delay in the action of a primer, igniter or propelling charge; for a few seconds it cannot be distingushed from a complete failure or misfire.

Hangfire Test

A test to determine uniformity and promptness of fire of a type of ammunition.

HC Mixture

Solid non-persistent screening smoke that, when burning, produces a grayish white smoke having a sharp, acrid odor; toxic if released in sufficient quantities in enclosed places; used in bombs, shells, grenades and smoke pots. The smoke is cool burning as contrasted with white phosphorous and tends to cling to the earth.

HE

High explosive (dynamite).

Heat

The internal Energy of a substance, associated with the positions and motions of its component molecules, atoms, and ions. The average kinetic energy of the molecules or atoms, which is due to their motions, is measured by the Temperature of the substance; the potential energy is associated with the state, or phase, of the substance ( States Of Matter). Heat energy is commonly expressed in Calories, British Thermal Units (BTU), or Joules, ( Work). Heat may be transferred from one substance to another by three means: Conduction, Convection, and Radiation. Also Heat Capacity; Specific Heat; Thermodynamics.

Originally an abbreviation for "high explosive antitank." A term used to designate high explosive ammunition containing a shaped charge. High-Explosive Antitank Shell.

Heat Capacity

Heat capacity or thermal capacity, ratio of the change in Heat energy of a unit mass of a substance to the change in Temperature of the substance. The heat capacity is a characteristic of a substance; it is often expressed in Calories per gram per degree Celsius or British Thermal Units per pound per degree Fahrenheit. Also Specific Heat.

Heat Of Combustion

Heat evolved in the complete oxidation of a substance under standard conditions of pressure and temperature.

Heat Of Explosion

Heat evolved in burning (exploding) a sample in a combustion bomb in an inert atmosphere under standard conditions of pressure and temperature. Products of explosion vary with the oxygen balance of the sample.

Heat Of Formation

Heat evolved, or absorbed, when a compound is formed by combination of its elements.

Heat Of Reaction

Heat evolved when a sample is burned in a combustion bomb in an atmosphere of helium or other inert gas.

Heat Test

Accelerated stability test of an explosive material.

Helium

(He), gaseous element, first observed spectroscopically in the sun during a solar eclipse in 1868. Its noncombustibility and buoyancy make this extremely unreactive, Inert Gas the most suitable of gases for balloons and airships. Deep-sea divers often breathe a helium-and-oxygen mixture; because helium is less soluble in human blood than nitrogen, its use reduces the risk of the bends. Liquid helium is essential for low-temperature work Cryogenics, Superconductivity. Helium is also used in arc welding and gas-discharge lasers. Abundant in outer space, helium is the end product of fusion processes in stars.

HEP Shell

High-Explosive Plastic Shell.

Hermetic Seal

A seal made impervious to air and fluids.

Hertz (Hz)

A synonym for “cycles per second”. Hertz, Heinrich Rudolf, 1857–94, German physicist. He confirmed James Clerk Maxwell’s electromagnetic theory and produced and studied electromagnetic waves (radio waves), which he showed are long transverse waves that travel at the speed of light and can be reflected, refracted, and polarized like light. The unit of frequency, the hertz, is named for him.

High-Angle Fire

Fire delivered at elevations greater than the elevation of maximum range, its range, therefore, decreasing as the angle of elevation is increased. Mortars deliver high angle fire.

High Explosive (HE)

Explosive which undergoes an extremely rapid chemical transformation thereby producing a high order detonation and shattering effect. High explosives are used as bursting charges for bombs, projectiles, grenades, mines and for demolition.

High Explosives

Explosives that are characterized by a very high rate of reaction, high pressure development, and the presence of a detonation wave in the explosive.

High Explosive Antitank (HEAT)

Shell Ammunition for defeat of armor by use of a shaped charge.

High Explosive Plastic (HEP)

Shell Shell with deformable nose, designed to contain a plastic explosive, for use against armor; shock transmitted through the armor causes the back of armor plate to spall. Also referred to as Squash-Head Shell.

High Explosive Shell

Projectile with a bursting charge of high explosive, used against personnel and material.

High Order Detonation

A detonation rate equal to or greater than the stable detonation velocity of the explosive.

Histogram

A graph whose axes are the frequency of measurements and the actual measured values.

Hivelite

A high velocity ignition propagation fuse (deflagrating).

HMX

Homocyclonite family; specifically cyclotetramethylenetetranitramine, the U.S name for Octogen, as an acronym for High Melting Explosive, and in the UK as Her Majesty’s Explosive. Octogen.

HNS

Abbreviation for hexanitrostilbene, also called hexanitrodiphenylethylene. A heat resistant explosive, commonly used in deep well charges found in the oil field or in applications requiring the explosive to withstand significant temperatures before initiation. C₆H₂(N0₂)₃. Molecular weight 450.24, nitrogen content 18.67%, melting point 316°C; detonating velocity 7000 m/s at density of 1.7 g/cc. Made in type I and type II and grades A and B. Differences between type I and type II is primarily the particle size (type I, 1-5 microns, type II, 100 - 300 microns). HNS has a uniquely small critical diameter of 0.020”. It is relatively insensitive to heat, spark, impact and friction, yet it finds wide use as a heat resistant booster charge for military applications.

Howitzer

A weapon firing slower than a gun and faster, but at lower angle, than a mortar.

Hubble's law

Hubble's law, statement that the greater the distance between any two Galaxies, the greater their relative speed of separation. In other words, the universe is expanding roughly uniformly. This empirical finding is more consonant with the big bang theory of the universe's origin than with the steady state theory ( Cosmology). The law was first proposed in 1929 by Edwin Hubble, who observed that the more distant a galaxy, the greater is its Red Shift and hence its velocity relative to our galaxy.

Hydrodynamics

The study of liquids in motion.

Hydrocarbon

A hydrocarbon is any organic compound composed solely of Carbon and Hydrogen. Hydrocarbons include aliphatic compounds, in which the carbon atoms form a chain, and Aromatic Compounds, in which the carbon atoms form stable rings. The aliphatic group is divided into alkanes (e.g., Methane and Propane), alkenes, and alkynes (e.g., Acetylene), depending on whether the molecules of the compounds contain, respectively, only single bonds, one or more carbon-carbon double bonds, or one or more carbon-carbon triple bonds. Petroleum distillation yields useful fractions that are hydrocarbon mixtures, e.g. Natural Gas, Gasoline, Kerosene, home heating oil, lubricating oils, Paraffin, and asphalt. Coal Tar is also a source of hydrocarbons. Hydrocarbon derivatives contain additional elements, e.g., oxygen, and include Alcohols, aldehydes, ketones, carboxylic acids, and halocarbons.

Hydrogen

Hydrogen (H) is a gaseous element, discovered by Henry Cavendish in 1766. The first element on the Periodic Table, hydrogen is colorless, odorless, tasteless, slightly soluble in water, and highly explosive. The hot flame produced by a mixture of oxygen and hydrogen is used in welding, and in melting quartz and glass. Normal hydrogen is diatomic ( Allotropy). The most abundant element in the universe, hydrogen is the major fuel in fusion reactions of the Sun and other Stars. Atmospheric hydrogen has three isotopes: protium (nucleus: one proton), the most common; deuterium, or heavy hydrogen (nucleus: one proton and one neutron), used in particle accelerators and as a tracer for studying chemical-reaction mechanisms; and tritium (nucleus: one proton and two neutrons), a radioactive gas used in the hydrogen bomb, in luminous paints, and as a tracer. Hydrogen's principal use is in the synthesis of Ammonia; liquid hydrogen has been greatly used as a rocket fuel, in conjunction with oxygen or fluorine. Deuterium oxide, or heavy water, is used as a moderator in nuclear reactors. Element.

Hydrogen Bomb

A weapon deriving a large portion of its energy from the nuclear fusion of hydrogen isotopes. In fusion, lighter elements are joined together to form heavier elements, and the end product weighs less than the components forming it. The difference in mass is converted into energy. Because extremely high temperatures are required to initiate fusion reactions, a hydrogen bomb is also known as a thermonuclear bomb. The presumable structure of a hydrogen bomb is as follows: an Atomic Bomb is surrounded by a layer of lithium deuteride (a compound of lithium and deuterium) and then by a tamper, or thick outer layer, frequently of fissionable material, that holds the contents together in order to obtain a larger explosion. The atomic explosion produces neutrons that fission the lithium into helium, tritium, and energy, and also produces the extremely high temperature needed for the subsequent fusion of deuterium with tritium, and tritium with tritium. Explosion of the neutron bomb, which has a minimal atomic trigger and a nonfissionable tamper, produces blast effects and a hail of lethal neutrons but almost no radioactive fallout. The first thermonuclear bomb was exploded in 1952 at Enewetak by the U.S., the second in 1953 by the USSR. Also Nuclear.

Hydrology

Hydrology, study of water and its properties, including its distribution and movement in and through the land areas of the earth. The hydrologic cycle consists of the passage of water from the oceans into the atmosphere; onto, through, and under the lands; and back to the ocean. Hydrology is mainly concerned with the part of the cycle that follows the precipitation of water onto the land and precedes its return to the oceans. Also Meteorology; Oceanography.

Hydrolysis

Hydrolysis is a chemical reaction of a compound with Water, usually resulting in the formation of one or more new compounds. The most common hydrolysis occurs when a salt of a weak acid or weak base (or both) is dissolved in water. Water ionizes into negative hydroxyl ions (OH^-) and positive hydrogen ions (H⁺), which become hydrated to form positive hydronium ions (H₃O⁺). The salt also breaks up into positive and negative ions, and the formed ions recombine.

Hygroscopicity

The tendency of a substance to absorb any available moisture from its surroundings; specifically the absorption of water vapor from the atmosphere.

Hydroxide

Hydroxide, chemical compound that contains the hydroxyl (-OH) radical. The term refers especially to inorganic compounds. Organic compounds that have the hydroxyl radical as a functional group are referred to as Alcohols. Most metal hydroxides are bases. Alkali Metals hydroxides, such as sodium hydroxide (NaOH), are strong bases and are very soluble in water. The Alkaline-Earth Metal hydroxides are less basic, and magnesium hydroxide (Milk of Magnesia) is only slightly basic. Some hydroxides, such as aluminum hydroxide {Al(OH)₃}, exhibit Amphoterism.

Hypergolic

A two-component propellant system which is capable of spontaneous ignition upon contact.

Hypervelocity

Muzzle velocity of an artillery projectile of 3,500 feet per second or more.

Hypervelocity Armor-Piercing (HVAP)

Ammunition Ammunition which embodies a core of hard, dense material (such as tungsten carbide) within a shell of light material (such as aluminum). Its light overall weight permits it to be fired safely at very high velocities. The velocity is rapidly lost, but at short ranges, it is effective against armor.

Hypervelocity Armor-Piercing Discarding Sabot (HVAPDS) Ammunition

Ammunition which embodies a Hypervelocity, armor-piercing subcaliber projectile within discarding sabot. Sabot.

Hypervelocity Armor-Piercing Discarding Sabot Fin-Stabilzed (HVAPDSFS) Ammunition

Ammunition which embodies hypervelocity, armor-piercing, subcaliber, fin-stabilized projectile within a discarding sabot. Sabot.

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