The second phase of a high altitude gun probe project is presented. The project objectives, the design considerations, the proof tests, the vertical tests and the dispersion of the system are discussed. An altitude capability of at least 240,000 ft. and an impact circle require ment of one-mile radius was demonstrated in two series of firings on the Edgewood peninsula of the Aberdeen Proving OUND. Although the performance of this fin-stabilized, five-inch projectile was proved, the tests indicate the need for further development of data packages and fuzes. (Author)