In February, 1946, The Jet Propulsion Laboratory (JPL) started to study the possibility of a two-stage research missile consisting of a V-2 first stage and a WAC Corporal as the second stage. The vehicle was planned to serve two purposes. First, it would be the first two-stage liquid-fueled rocket ever built, and as such would explore problems related to stage separation and rocket ignition at high altitude. Second, it would greatly increase the maximum altitude reached by a small research rocket.
For this project the WAC Corporal had to be extensively modified which led to its designation as the Bumper WAC. Four large fins replaced the original three smaller ones, and additionally had two small solid-fueled spin motors to induce gyro-stabilizing spin for the exo-atmospheric flight. The staging mechanism worked by reducing the V-2 engine’s thrust at a predetermined speed, followed by a signal to the Bumper WAC to ignite its engine. The latter burned through a wire, thereby signaling V-2 engine cutoff. With the V-2 decelerating, the upper stage could slide out on its rails and begin free flight.
The first flight of a live Bumper WAC took place on September 30. 1948, but failed because the WAC’s engine exploded on ignition. After tracking down a design deficiency and correcting it, on February 24, 1949, a first successful mission was accomplished. On that day, the upper stage reached an altitude of 244 miles, a new record for any man-made object. That record stood for several years.
When two vehicles remained in the inventory, the Bumper WAC was used to produce aerodynamic data at unprecedented speeds. For this purpose, the V-2 would fly an arched trajectory and release the Bumper WAC in almost horizontal attitude. These tests needed a firing range with a large open unpopulated area and Cape Canaveral in Florida was selected. The Bumper became the “founding father” for the world’s most famous space launch facility. On its second and final attempt, on July 29, 1950, the Bumper WAC reached a speed of 3270 MPH.
Source: Excerpted from “General Electric RTV-G-4 Bumper” document.