In 1951 Lockheed built this ramjet test bed for the United States Air Force. The X-7, or Flying Stove Pipe was launched from the bottom of a B-50 or a B-29. The Rocket assist slung under the thin and long fuselage was ignited and that propelled the jet to about Mach 1.5, feeding the ramjet. Once the Ramjet was engaged the plane accelerated to 2880 miles per hour or roughly Mach 4. Over 130 of these flights were successfully made for a period covering almost 20 years.
It was 32 feet long and only had a 12 foot wingspan, almost the mold for fast interceptors that would follow like the F-104. It’s service ceiling was outer space at 106,000 feet.
Sources: Lockheed, Wikipedia