T40 Whizbang

The Rocket Launcher T40/M17 (Whizbang) (sometimes spelled "WhizBang") was a tank-mounted multiple rocket launcher used by the United States Army during World War II. The launcher was placed atop the Medium Tank M4, and fired a barrage of 7.2 in (180 mm) T37 HE or T21 Chemical rockets from 20 launch tubes. It was developed and used in the late stages of World War II; it saw limited combat in 1944–45. An experimental short variant of the T40 was also developed.
Design.
The rocket launcher on the T40/M17 WhizBang could hold twenty 7.2-inch rockets in a box-like frame, which could be elevated hydraulically with the controls for the 75 mm gun. The whole-mount could be jettisoned, if needed. If jettisoned, the 75 mm gun could be used as normal. The rockets in the mount could be fired one-at-a-time or in salvoes. The T40 was a "limited procurement" weapon that was later classified as "limited standard".
Service history.
T40s saw limited use in the European Theater in 1944–1945. They were originally intended to be used on D-day, but delays in testing meant that final approval of the design occurred too late for use in the Normandy Invasion. Testing also showed that the rockets were potentially dangerous to both the launcher crew and to anyone else in the vicinity. The Marine Corps examined the T40 for possible use in the Marianas Campaign in 1944, but ultimately it was not used in the Pacific.
In December 1944, thirty T40s were put into service on the Ardennes Front. A large German counter-attack in that sector caused the T40s to be redeployed to safer positions. After the battle, the T40s were redeployed to northern Italy where they remained for the remainder of the war.
The Army authorized the manufacture of 1,000 kits to convert standard M4 Medium Tanks to T40s, but only two conversions actually occurred. Ultimately continuing delays in the project led to its cancelation.
T40 (short version).
The T40 (short version) was an experimental version of the T40 that featured shorter rocket tubes and removed the main gun. In place of the main gun, an elevation mechanism for the rocket launchers was installed. This version also featured a side access door for the crew.