other armor often has a shaped charge explosive warhead. A shaped charge is an explosive charge shaped to focus the effect of the explosive's energy. Various types are used to penetrate tank armor; typical modern lined shaped charge can penetrate steel armor to a depth of seven or more times the diameter of the charge (charge diameters, CD), though greater depths of 10 CD and above have been achieved. Despite the popular misconception that shaped charges "melt" tank armor, the shaped charge does not depend in any way on heating or melting for its effectiveness; that is, the superplastic metal jet from a shaped charge impact on armor forms mainly due to a sudden and intense mechanical stress and does not melt its way through armor, as its effect is purely due to kinetic energy in nature. An RPG comprises two main parts: the launcher and a rocket equipped with a warhead that follows a ballistic trajectory after the rocket motor has completed its burn. The most common types of warheads are high explosive (HE) and high-explosive anti-tank (HEAT) rounds. HE rounds can be used against troops or unarmored structures or vehicles. HEAT rounds can be used against armored vehicles. These warheads are affixed to a rocket motor and stabilized in flight with fins. Some types of RPG are single-use disposable units, such as the RPG-22 and M72 LAW; with these units, once the rocket is fired, the entire launcher is disposed of. Others are reloadable, such as the Soviet RPG-7 and the Israeli B-300. With reloadable RPGs, a new rocket can be inserted into the muzzle of the weapon after firing. An issue that affected the earliest RPG weapon systems such as the German Panzerschreck was that rocket motor propellant could harm the operator. The weapon therefore featured a metal shield attached to the launch tube to protect the operator’s face from the blast. With later designs such as the RPG-7, the rocket exits the launcher with a low-powered gunpowder charge, and the main rocket motor then fires after the rocket has travelled . In some other designs, the propellant charge burns completely within the tube. An RPG is an inexpensive way for an infantryman to safely deliver an explosive payload or warhead over a short distance with reasonable accuracy. Substantially more expensive guided anti-tank missiles are used at larger distances when accuracy or an overfly top attack are