The American plane designed for this role was the Northrop XP-79B. Started as a program to develop a rocket-powered gun-equipped fighter, the XP-79B emerged as a magnesium-reinforced jet designed to ram enemy aircraft. The jet's design was unique, placing the pilot in a prone position to allow him to endure much greater g-forces. The pilot controlled the ailerons with a tiller bar in front of him and rudders mounted at his feet, which is the reverse of normal flight controls. Intakes at the wingtips supplied air for the unusual bellows-boosted ailerons.
Naturally the plane was nicknamed the "Flying Ram." The plan was simple: fly above enemy aircraft, then enter a high-speed dive and collide with an enemy's wing or vertical stabilizer. The XP-79B was designed to survive because of the heavily reinforced leading edges on the wings.
Fortunately for potential pilots, the balance of power in the war turned against the Axis before the plane ever flew. The only XP-79B to take to the air did so after the war's end, and ended tragically. Test pilot Harry Crosby had flown the plane well for several minutes before it entered an uncontrollable spin from 8,000 feet, and Crosby was unable to bail out. The XP-79B project died with him.
Although Axis pilots-- especially the Japanese-- actually did try to collide with Allied bombers using volunteers using conventional aircraft, they also had efforts to develop ramming planes. The Zeppelin Company in Germany-- named after Count Ferdinand von Zeppelin-- was working on such a rocket plane when the war ended. It was called the Zeppelin Rammer.
The Rammer was proposed in the last six months of the war, but its progress never went beyond the design stage. Unlike the XP-79B, the Rammer was to be towed aloft by another fighter (probably a ME-109 or ME-110) and then released at the desired altitude. After being released it would ignite a solid-fuel rocket and accelerate to six hundred miles per hour. The small plane had fourteen small rockets housed in the nose, which could be fired at an enemy aircraft. The fighter could then take a second pass to ram the target if needed.
The Japanese never got to the stage of designing a plane specifically for ramming. Still, some Allied B-29's were lost in ramming attacks by Japanese pilots using outdated aircraft. The Shinten Seiku-tai (The Heaven Shaking Air Superior Unit) were specially trained sections of fighter units with the mission of air-to-air ramming of Allied bomber aircraft. It was all an act of desperation which had no significant military value aside from downing a few bombers, much like the kamikazes' efforts to damage US carriers.
The idea of using an aircraft as a manned guided missile has a modern footnote as well. On September 11, 2001, F-16 pilots flying combat air patrol over Washington DC decided that they would ram hijacked airliners if necessary. The pilots had taken off in such a hurry to protect Washington that they left with no air-to-air missiles and the wrong ammunition. Some planes left with non-explosive practice rounds.
Although the Northrop XP-79B program was cancelled early, its legacy lives on in the 21st century. The Northrop Corporation ultimately used its basic design when building the revolutionary "Flying Wings" of the 1950s. Northrop gained considerable knowledge about wing-only aircraft with planes like the XP-79B, and that expertise eventually lead to the B-2 Stealth Bomber.