The Applied Physics Laboratory of Johns Hopkins University had done important wartime research for the Navy. A staff scientist, James van Allen, wanted a research rocket that was smaller and less costly than the V-2. His inquiries led him to the California firm of Aerojet, which was already building small rockets for the Army. In May 1946, the Navy's Bureau of Ordnance gave Aerojet a contract to build a new one, the Aerobee, that could carry 150 pounds (68 kilograms) of instruments to an altitude of 70 miles (113 kilometres). The first of them flew in November 1947.

The German team of specialists was initially assigned to Fort Bliss, Texas, where they reassembled and tested V-2 rockets brought to America from Germany; later they came to the army's Redstone Arsenal in Huntsville, Alabama.

The Naval Research Laboratory (NRL) also sought to build a larger rocket, called Viking, that could carry 500 pounds (227 kilograms) of instruments above 100 miles (161 kilometres). Milton Rosen, an NRL electronics specialist, pushed this project through the Navy bureaucracy and arranged for the Martin Company, a large builder of aircraft, to build this new rocket. Its engine, which came from the New Jersey firm of Reaction Motors, had 20,000 pounds (88,964 Newtons) of thrust. The first three Vikings flew during 1949 and 1950. These travelled no higher than 50 miles (80 kilometres), but subsequent shots were fully successful.

 
In May 1950, the Office, Chief of Ordnance assigned Redstone Arsenal responsibility for the preliminary design study for the special purpose, large calibre field artillery rocket later named the Honest John.

Viking and Aerobee carried cameras, sometimes with colour film. Their photos gave astronauts'-eye views of the Earth long before there were astronauts, showing the subtle brown and green hues of desert and fertile land. High over El Paso, Texas, with the horizon more than 1,000 miles (1,609 kilometres) away, Viking cameras captured much of Mexico and showed the Pacific Ocean, beyond Baja California. Views of clouds encouraged the thought that photos from space could be useful in weather prediction.

 
On July 24, 1950, the first Army missile was launched from Cape Canaveral, Florida. Bumper Round 8 attained a horizontal distance of 25 miles. The first-stage V-2 climbed 10 miles, successfully separating from the second-stage WAC Corporal, which travelled another 15 miles.

At the aircraft firm of Convair in San Diego, the manager Karel Bossart set out to build a rocket for the Air Force. Postwar budgets were very tight, but Bossart came up with $1.9 million, which was enough for a good start. He deliberately copied the shape of the V-2, to allow his designers to use German data in their studies. That German rocket had used an engine with nearly 60,000 pounds (266,893 Newtons) of thrust, but Bossart needed only 8,000 pounds (35,586 Newtons) because his rocket was smaller than the V-2 and much lighter. He used an existing engine that also came from Reaction Motors.

The Air Force called his rocket the MX-774, and Bossart aimed for an altitude of 100 miles (161 kilometres). Three MX-774s flew during 1948, but all experienced premature engine cut-off and reached only 30 miles high. Following the third flight, his engineers found the problem and hoped for a fourth launch that might be successful. But there was no money left in the budget, and Bossart had to abandon his project.

At North American Aviation in Los Angeles, another aircraft firm, the chairman James Kindelberger had greater ambitions. He saw his company's future as lying in rockets, missiles, and supersonic jet planes. He needed specialists in propulsion, guidance, aerodynamics, and advanced electronics, and he knew that the way to attract them was to bring in the best scientist he could find and have him build up a new research centre. This man was William Bollay, who had helped the Navy build jet fighters during the war. Bollay came to Los Angeles late in 1945.

Neither the Viking nor the MX-774 approached the power of the V-2, but Bollay wanted to use that rocket as his starting point. Late in the war, Von Braun had tried to stretch the range of this missile by adding wings. Bollay's concept, called the Navaho, resembled this winged V-2 but used original research in supersonic aerodynamics to make it fly better. To increase its range to as much as 1,000 miles (1,609 kilometres), the design called for ramjet engines that were to be mounted at the tips of its fins.

Bollay left the ramjets to another company, Wright Aeronautical, but took the rockets as his own project. Bollay also wanted to test full-size V-2 engines, and company executives helped him by purchasing land for a major rocket test centre. The Air Force provided funding, and Bollay decided to develop a new engine of 75,000 pounds (333,617 Newtons) of thrust. Tests at full power began in March 1950. Within months, it was working well.

Just then, the Army was pursuing its own advances, which had the Nike antiaircraft missile under contract at Bell Labs. The Army also was building the solid-fueled “Honest John” rocket for use on battlefields. Also, its Jet Propulsion Laboratory in California was at work on the liquid-fuelled Corporal, with its planned range of 60 miles (97 kilometres). In 1949 the Army set up a new rocket center at Redstone Arsenal in the farm town of Huntsville, Alabama. Von Braun and his men arrived a year later, in April 1950.

Two months later, war broke out in Korea, and the United States almost immediately sent forces into the conflict. With the Nation once more at war, missiles took on new urgency. Von Braun won permission to develop the Redstone missile, which was to carry an atomic bomb to a distance of 200 miles (322 kilometres). He needed an engine, and found what he wanted in Bollay's rocket of 75,000 pounds (333,617 Newtons) of thrust. The Redstone made its first test flight in August 1953.

The outbreak of war also gave new importance to Navaho. By 1950, the V-2 appeared old fashioned, and Air Force officials wanted something entirely new. Bollay's designers responded with plans for winged Navahos with ranges of 3,000 (4,828 kilometres) and even 5,500 miles (8,851 kilometres). The 75,000-pound (333,617-newton) engine now no longer had the thrust these missiles needed. Sam Hoffman, the top rocket man at North American, came forward with a design for a new engine with 120,000 pounds (533,787 Newtons) of thrust. Two of these were to power the 3,000-mile Navaho; three would boost the 5,500-mile version.

The Korean War also led the Air Force to take a new look at the plans of Convair's Karel Bossart, who wanted to build a rocket with a range of 5,000 miles (8,047 kilometres). In contrast to the winged Navaho, this was to be a ballistic missile, flying without wings like an enormous artillery shell. In December 1950 the Rand Corporation, which provided the Air Force with technical advice, reported that the technology for such a missile would soon be in hand. Air Force officials nevertheless held back. Bossart's missile was to carry an atomic bomb, but the warheads of the day were very heavy. Hence this missile would be unacceptably large, and too unwieldy to transport. It also needed high accuracy in its guidance, but suitable guidance systems lay well in the future.

Then came a breakthrough: the hydrogen bomb. The first of them, detonated in November 1952, had nearly a thousand times the energy of the first atomic bomb. Secret studies, conducted during 1953 and 1954, showed that hydrogen bombs could be far lighter in weight than existing atomic weapons, while delivering far more explosive force. Tests of such weapons, conducted during 1954, showed that they not only could meet their goals but also could actually run out of control, yielding far more energy than predicted.

In one swoop, this breakthrough completely changed the prospects for ballistic missiles. The modest weight of the new weapons now meant that the missiles could be much smaller. Nor did they need precision guidance. The warhead might miss its target by up to three miles and still destroy it by the simple method of wiping out everything that lay between the aim point and the impact point. Bossart's missile already had the name Atlas. In May 1954 the Air Force gave it top-priority go-ahead for development.

North American B-64 "Navaho" Launch view, June 26, 1957, the fourth launch of a Navaho

These engines and missiles soon took on new roles. The 120,000-pound Navaho engine had its thrust increased to 150,000 pounds (667,223 Newtons) and provided propulsion for the Atlas. This engine also powered the Thor and Jupiter missiles, with the latter a project that Von Braun pursued after finishing with Redstone. Aerojet built a similar engine for the Titan missile, which had more power than the Atlas. Thor, Atlas, and Titan soon became launch vehicles for space flight, carrying spacecraft and astronauts into orbit.