The earliest rocket launchers documented in imperial China consisted of arrows modified by the attachment of a rocket motor to the shaft a few inches behind the arrowhead. The rocket is propelled by the burning of the black powder in the motor. (These rockets should not be confused with “rocket arrows” which are conventional arrows carrying small tubes of black powder as an incendiary that ignites only after the arrow reaches its target. A fuse is lit before release of the arrow. ) The rocket launchers were constructed of wood, basketry, and bamboo tubes. The launchers divided the rockets with frames meant to keep them separated, and the launchers were capable of firing multiple rockets at once. Textual evidence and illustrations of various early rocket launchers are found in the 1510 edition of the Wujing Zongyao translated by Needham and others at Princeton University. (The original Wujing Zongyao was compiled between 1040 and 1044 and described the discovery of black powder but preceded the invention of the rocket. Partial copies of the original survived and Wujing Zongyao was republished in 1231 during the Southern Song Dynasty, including military developments since the original 1044 publication. The British scientist, sinologist, historian Joseph Needham asserts that the 1510 edition is the most reliable in its faithfulness to the original and 1231 versions, since it was printed from blocks that were re-carved directly from tracings of the edition made in 1231 AD. ) The 1510 Wujing Zongyao describes the “long serpent” rocket launcher, a rocket launcher constructed of wood and carried with a wheelbarrow, and the “hundred tiger” rocket launcher, a rocket launcher made of wood and capable of firing 320 rocket arrows. The text also describes a portable rocket carrier consisting of a sling and a bamboo tube.