Recoilless rifle
The largest versions retain enough bulk and recoil to be restricted to a towed mount or relatively heavy vehicle, but are still much lighter and more portable than cannon of the same scale.
The earliest known example of a design for a gun based on recoilless principles was created by Leonardo da Vinci in the 15th or early 16th century.
The Luftwaffe also showed great interest in aircraft-mounted recoilless weapons to allow their planes to attack tanks, fortified structures and ships.
These included the unusual Düsenkanone 88, an 88 mm recoilless rifle fed by a 10-round rotary cylinder and with the exhaust vent angled upwards at 51 degrees to the barrel so it could pass through the host aircraft's fuselage rather than risking a rear-vented backblast damaging the tail, and the Sondergerät SG104 "Münchhausen", a gargantuan 14-inch (355.6 mm) weapon designed to be mounted under the fuselage of a Dornier Do 217.
Postwar saw a great deal of interest in recoilless systems, as they potentially offered an effective replacement for the obsolete anti-tank rifle in infantry units.
Postwar work developed and deployed the BAT (Battalion, Anti Tank) series of recoilless rifles, culminating in the 120 mm L6 WOMBAT.
The large crew-served recoilless rifle started to disappear from first-rate armed forces, except in areas such as the Arctic, where thermal batteries used to provide after-launch power to wire-guided missiles like M47 Dragon and BGM-71 TOW would fail due to extremely low temperatures.
First introduced in 1948 and exported extensively since 1964, it is still in widespread use throughout the world today: a huge selection of special-purpose rounds are available for the system, and the current variant, known as the M4 or M3E1, is designed to be compatible with computerized optics and future "smart" ammunition.
Many nations also use a weapon derived from the Carl Gustav, the one-shot AT4, which was originally developed in 1984 to fulfil an urgent requirement for an effective replacement for the M72 LAW after the failure of the FGR-17 Viper program the previous year.
The ubiquitous RPG-7 is also technically a recoilless gun, since its rocket-powered projectile is launched using an explosive booster charge (even more so when firing the OG-7V anti-personnel round, which has no rocket motor), though it is usually not classified as one.
The most basic method, and the first to be employed, is simply making a double-ended gun with a conventional sealed breech, which fires identical projectiles forwards and backwards.
Despite the name, it is rare for the forces to completely balance, and real-world recoilless rifles do recoil noticeably (with varying degrees of severity).
Recoilless rifles will not function correctly if the venting system is damaged, blocked, or poorly maintained: in this state, the recoil-damping effect can be reduced or lost altogether, leading to dangerously powerful recoil.
The casing of a recoilless rifle round is often perforated to vent the propellant gases, which are then directed to the rear by an expansion chamber surrounding the weapon's breech.
Recoilless gun launch systems are often used to provide the initial thrust for man-portable weapons firing rocket-powered projectiles: examples include the RPG-7, Panzerfaust 3 and MATADOR.
The Armbrust "cartridge," for example, contains the propellant charge inside a double-ended piston assembly, with the projectile in front, and an equal countermass of shredded plastic to the rear.
They were then replaced with M40 106 mm recoilless rifles, but following a catastrophic in-bore ammunition explosion that killed one of the five-man gun crew at Alpine Meadows Ski Resort, California, in 1995 and two further in-bore explosions at Mammoth Mountain, California, within thirteen days of each other in December 2002, all such guns were removed from use and replaced with surplus 105 mm howitzers.
