various semi-automatic designs, mostly gas operation and recoil operation designs. The SPAS-12, SPAS-15, and Benelli M3 shotguns, combine the two, offering pump action or, when the pump is locked forwards, autoloading operation. There have also been a few fully automatic shotguns produced such as the AA-12. The autoloading shotgun (semi or fully automatic) offers a higher rate of fire than a pump shotgun, though controlling a heavy recoiling shotgun in rapid fire is difficult. The autoloading action is more suitable for firing from a prone position, as operation of a pump action moves the elbow normally used to support the shotgun, and it can more effectively be used one-handed, unlike pump actions which require two hands for effective cycling of the action. The pump shotgun is more versatile than the semiautomatic, as it will fire low powered less lethal munitions which lack sufficient pressure to cycle the action in an autoloading design. A pump shotgun, which does not rely on its ammunition for energy to cycle, operates normally with the lower powered ammunition, and provides utility in combat and riot control situations. In addition, the pump shotgun has an advantage in situations such as door breaching, where the shotgun is immediately dropped (retained by a sling) and replaced by another weapon after the door has been breached. By not cycling the action after firing the final breaching rounds (multiple rounds are often required) the pump shotgun is left without a loaded round in the chamber, unlike a semiautomatic shotgun. Use in asymmetric warfare Due to the widespread use of the shotgun as a sporting firearm, it is used in guerrilla warfare and other forms of asymmetric warfare. Che Guevara, in his 1961 book Guerrilla Warfare, notes that shotgun ammunition can be obtained by guerrillas even in times of war, and that shotguns loaded with heavy shot are highly effective against unarmored troop transport vehicles. He recommends that suburban guerrilla bands should be armed with easily concealable weapons, such as handguns and a sawed-off shotgun or carbine. Guevara also mentions an improvised weapon developed by guerrillas consisting of a sawed-off 16-gauge shotgun provided with a bipod to hold the barrel at a 45 degree angle. Called the "M-16", this was loaded with a blank cartridge formed by removing the shot from a standard shotshell. A wooden rod was then placed in the barrel, with a Molotov cocktail attached to the front.