Das SLV Juno-II wurde von der NASA alternativ zur Juno-I entwickelt. Im Unterschied zur Juno I (Redstone) wurde als Grundstufe die Jupiter PGM 19A (SM-78) der USArmy verwendet.
Die Jupiter hatte ein bedeutend höheren Schub und aufgrund des Durchmessers ein größeres Fassungsvermögen für Treibstoff. Die Tanks der PGM 19A waren um insgesamt 0,91 m verlängert worden. Die Konstruktion bestand aus Stahlblech. Als Antrieb diente ein schwenkbares Triebwerk Rocketdyne S - 3D, das später als Standard bei dem SLV Thor eingesetzt wurde (LR-79-NA-9). Als Treibstoffkombination wurde Kerosin (RP-1)/Sauerstoff verwendet.

Die Oberstufenkombination (Köcher mit 15 Feststofftreibsätzen) wurde beibehalten. Der Köcher befand sich jedoch in einer Zelle mit einem konischen Shroud.
Von 1958 bis 1961 wurden 10 Starts durchgeführt, von denen jedoch nur die Hälfte erfolgreich war.

The work of developing the Jupiter was handled by the NASA and the Army Ballistic Missile Agency in 1955.
The Juno-II was a single-stage vehicle Jupiter with a length of 60.3 ft. and a fuelled weight of 110.000 lb using an Rocketdyne S-3D engine having a thrust of 150.000 lb. The body was essentially a cylinder of metal construction with a diameter of 105 in. made by Chrysler Corporation.
Development of the S-3 engine began in November 1955 by North American Rocketdyne. The engine itself  was similar to that of the Thor's main engine, the LR-79-NA-9, except that the generator exhaust was expelled from a nozzle, acting both as vernier and roll control in the launcher , the S-3D (a refined version of S-3 from LOX and Kerosene RP-1) was gimbal-mounted, providing course control. To increase the tankage volume and burn time, the Jupiter had its main body lengthened by 3 ft., giving it additional fuel for 20 seconds extra thrust. All-up weight was increased  to 121.000 lb.
The three upper stages were all formed from various configurations of scaled-down Sergeants in the same manner as used with Juno I (Redstone). The second and third  stage, with eleven and three Sergeants respectively, were placed together to form a tub, with the third stage nestling inside the outer ring of the second. Because a solid fuel motor could not be relied upon to perform the same as any other in its family, the whole assembly, with a single Sergeant mounted centrally and above the others, was spun up before launch to even out any irregularities in thrust. This drum, spun by two electric motors, was enclosed in a shroud for protection against aerodynamic forces.
After the S-3D main engine had fired for 182 seconds the upper stages separated. Then the payload shroud was blown away by explosives the Sergeants to begin their firing. The stages fired at nine second intervals.
With this configuration, Juno II was able to take 110 lb. to LEO  or put 15 lb. on an Earth escape trajectory.