FOR TRAINING USE ONLY TST-204 Self-Propelled Artillery Weapon (SPAW) Artillery Tutorial Introduction The following is a brief tutorial on artillery nomenclature and operation, to assist you in understanding the TST-204 exercise material. The purpose is not to make you artillery testers, but to give you just enough background information so you recognize key elements of the SPAW system and its operation, and so you don’t get distracted by unfamiliar terms. This tutorial is organized into four main areas to cover the basics of artillery gun types, artillery operation, gunnery fundamentals, and artillery organization. The explanations and definitions in this tutorial come from various sources, with the majority of the information from the Army Field Manual (FM) 6-40 “Tactics, Techniques, and Procedures for Field Artillery Manual Cannon Gunnery”. The student is encouraged to use official current guidance for more detailed information; or prior to real-world operation or test and evaluation of artillery systems. Army FM 6-40 provides a concise statement of the mission of Field Artillery – “The mission of the Field Artillery is to destroy, neutralize, or suppress the enemy by cannon, rocket, and missile fires and to help integrate all fire support assets into combined arms operations.” The SPAW system provides cannon fire to accomplish its portion of the field artillery mission. The term “cannon” is a general term used when referring to artillery. It refers to an artillery gun or a howitzer, which are defined below. Artillery Gun Types Artillery generally refers to large-caliber weaponry that are operated by a crew, as opposed to small arms or weaponry carried and fired by individual troops. Types of artillery include: Guns – Which fires at a high muzzle velocity through relatively long barrels and with a flat trajectory. Examples would be antiaircraft or antitank guns. Howitzers – Artillery weapons that have relatively short barrels, lower muzzle velocities, and more parabolic trajectories. Mortars – Generally small tactical munitions fired from short tubes. Mortars are fired with a high trajectory and have a relatively short range. FOR TRAINING USE ONLY Figure 1: Typical Trajectories (Field Manual 6-40) Artillery is usually ranked as light, medium, or heavy. Light refers to projectiles up to 105mm for close support of ground troops, medium at 106 – 155mm for bombardment, and heavy, with projectiles over 155mm for attacking rear installations. Artillery is also classified according to the method of ground transportation, either towed or self-propelled. Towed artillery is mounted on carriages and is designed to be towed behind other vehicles. Self-propelled artillery is mounted on tracked vehicles, and can move between firing positions under its’ own power. Towed artillery is generally lighter than self-propelled, but obviously requires a separate vehicle to tow it. Self-propelled artillery can be quicker to reposition to a new firing position. Artillery Gunnery Fundamentals There are some fundamental principles involved in operating artillery. The following are five basic requirements for achieving accurate artillery fire. The five basic requirements are: a. Target Location and Size. Establishing the range from the artillery weapons to the target requires accurate and timely detection, identification, and location of ground targets. Determining the appropriate time and type of attack requires that the target size (radius or other dimensions), makeup (i.e., troops, vehicles, bunker, etc), and the direction and speed of movement be considered. b. Firing Unit Location. Accurate aiming to the target requires accurately knowing artillery firing unit locations. There are different ways to determine the firing unit location, such as Global Positioning System (GPS) or site surveys. In addition to determining an accurate location for the firing unit, each howitzer in the firing unit must also be precisely positioned to make sure each projectile goes exactly where it was intended. One term that is prevalent in almost all weapon firing discussions is a mill radian – usually referred to as a “mil.” A mil is a measure of angle. Using a circle of 360 degrees does not provide enough precision, therefore artillery computations assume a complete circle is broken into 6400 mils. Pointing a howitzer requires two angle commands (given in mils): azimuth (horizontal direction FOR TRAINING USE ONLY measured from north) and elevation (vertical angle measured from level). In a practical sense, one mil of elevation or azimuth works out to be a change of one meter at a range of 1000 meters. c. Weapon and Ammunition Information. The actual performance of the weapon is measured by the weapon muzzle velocity (velocity with which the projectile leaves the muzzle of the tube) for a projectile-propellant combination. The firing battery can measure the achieved muzzle velocity of a weapon and correct it for nonstandard projectile weight and propellant temperature. A howitzer can fire different types of projectiles, depending upon the target, and each projectile can be fired with different propellant loads. The combinations can put different stresses on the artillery piece, which must be factored into the design, operation, and maintenance of the artillery system. (See the discussion on error sources below for additional details on common weapon and ammunition issues affecting cannon performance.) d. Meteorological Information. The effects of weather on the projectile in flight must be considered, and firing data must compensate for those effects. e. Computational Procedures. The computation of firing data must be accurate. Manual and automated techniques are designed to achieve accurate and timely delivery of fire. If these five requirements are met, the firing battery will be able to deliver accurate and timely fires in support of the ground troops. If the five requirements for accurate predicted fire cannot be met, changes can be made to compensate for nonstandard conditions. Sources of Error The five basic requirements provide for accurate artillery fire. Now let’s briefly address factors which can make it difficult to meet the requirements and hence adversely affect the accuracy of fire. The first major source of error is in the initial set-up and aiming of each artillery piece. If the howitzer is set up on perfectly level ground, then the error would be primarily from errors in location or misalignment of the zero point in azimuth. Since it is difficult to find perfectly level ground, then the set-up would also need to consider the slope of the terrain. Up or down slopes along the line of fire can introduce elevation errors. Slopes to the right or left of the line of fire, introduce leaning errors called “cant.” Cant causes errors in both azimuth and elevation. Artillery weapons must have an ability to correct for less than perfect site conditions, and they can compensate with mechanical means to level the weapon, and/or through corrections in the firing computations. If the artillery piece is properly sited, then the next major source of errors comes from unintended variations in firing the howitzer. Since muzzle velocity is the parameter usually measured to determine performance of the howitzer, FOR TRAINING USE ONLY anything that affects muzzle velocity becomes a potential error source. Nonstandard muzzle velocity is expressed as a variation (plus or minus so many meters per second) from the accepted standard. This figure illustrates how a tube’s standard muzzle velocity (m/s-meters per second) can vary from round to round depending on how the tube is cleaned. Some of the primary factors affecting muzzle velocity are: • Tolerances in new weapons. All new cannons of a given caliber and model will not necessarily develop the same muzzle velocity. Calibration of all cannons allows the firing unit to compensate for small variations in the manufacture of cannon tubes and the resulting variation in developed muzzle velocity. Once determined, the muzzle velocity variation caused by inconsistencies in tube manufacture remains constant and is valid for the life of the tube. • Tube wear. Continued firing of the cannon wears away portions of the bore by the actions of hot gases and chemicals and movement of the projectile within the tube. These erosive actions are more pronounced when higher charges are fired. The greater the tube wear, the more the muzzle velocity decreases. Normal wear can be minimized by careful selection of the charge and by proper cleaning of both the tube and the ammunition. • Propellant and projectile temperatures. Any combustible material burns more rapidly when heated before ignition. When a propellant burns more rapidly than would be expected under standard conditions, the muzzle velocity will be greater than standard and the projectile will travel farther. FOR TRAINING USE ONLY The time and type of exposure to the weather result in temperature variations from round to round and within the firing unit. • Moisture content of propellant. Since the moisture content cannot be measured or corrected for, the propellant must be provided maximum protection from the elements and from improper handling. • Weight of the projectile. In general terms, a heavier-than-standard projectile normally experiences a decrease in muzzle velocity. A lighter- than-standard projectile generally experiences an increase in velocity. • Coppering. When a projectile is fired, a thin film of material is left within the bore and is known as coppering. The amount of copper deposited varies with velocity. Firing higher charges increases the amount of copper deposited on the bore surfaces, whereas firing lower charges reduces the effects of coppering. Excessive coppering causes erratic velocity performance and must be removed by ordnance personnel. • Tube conditioning. The temperature of the tube has a direct bearing on the developed muzzle velocity. A cold tube offers a different resistance to projectile movement and is less susceptible to coppering, even at high velocities. In general, a cold tube yields more range dispersion; a hot tube, less range dispersion.