The Skysweeper

New Tool for the Antiaircraft Artilleryman

The Department of Defense has removed the wraps from its newest and largest caliber automatic weapon to be produced to date. Here are the facts and a glimpse at the Army's most recent addition to its arsenal of weapons—a 75mm artillery machine gun—the most effective weapon against low-flying, high-speed aircraft.

Recently the Department of Defense raised the curtain on a new automatic antiaircraft artillery weapon which is virtually an artillery machine gun. This new weapon, nicknamed the Skysweeper, is the first of its kind to have radar, computer and gun on one carriage. It is likewise the first of its kind to be fully integrated with fire control and fire power. Its capabilities include spotting and tracking with radar at a maximum distance of 15 miles, and aiming and firing the gun automatically at any enemy aircraft flying at near sonic speed at a distance of four miles. In addition, it can be used against moving ground targets. These capabilities can be accomplished regardless of the weather or when the aircraft are invisible. In the event of mass targets, selection can be made by the operator. This mobile unit is towed by a cargo tractor. It can be emplaced and have its radar operating in five minutes regardless of the type of terrain. The unit weighs ten tons and is air transportable. In traveling position it is 25 feet long, eight feet wide, and seven feet high.

The gun is a 75mm antiaircraft with automatic loading and firing features combined. The gun fires high explosive shells weighing approximately 12½ pounds each, at a rate of 45 rounds per minute. This type of shell armed with a proximity fuse explodes automatically at a predetermined distance from the target. The ammunition is automatically fed and rammed into the gun from two eleven-round magazines by an electrically operated loader rammer. The firing can be controlled remotely by either the radar or computer operators. The counter recoil movement automatically opens the gun breech.

The radar unit is equipped to automatically sweep the entire sky once every 40 seconds, detecting aircraft in its 15-mile radius, and graphically showing as a blip on a cathode ray picture tube in the radar control panel. This target information is automatically transmitted to the electro-mechanical computer. The radar unit is in a large console mounted to the left of the gun tube in the front corner of the carriage, surmounted by a dishpan antenna. Two picture tubes are visible on the rear side of the console. One is used for scanning and the other for tracking.

The computer automatically plots the range, speed and course of the approaching target, determining where the gun must point so that when a shell is fired it will hit the target. In other words, the “lead,” necessary in firing at a moving target, is automatically built in. The computer is located in a large console mounted to the right of the gun tube in the right front corner of the carriage and automatically feeds future target position data into a power control which translates it into corresponding gun motion.

The integrated units discussed above are all mounted on a combination chassis and gun mount with 4 wheels. These are removed along with the axles emplacing the gun. Specially designed shock absorbers permit towing over rough ground by a prime mover which is usually the M8 Army cargo tractor. The mount can be emplaced on uneven ground or on a slight slope. A motor-driven hydraulic jack lowers the carriage to the ground. Reversing the jack raises the carriage. A rigid pedestal and 4 retractable outriggers extend from the mount when the weapon is emplaced.

A target selector which is an auxiliary sighting device is used to direct the gun to more advantageous targets which might have been missed by the gun operators. This selector is considered to be a piece of off mount equipment. Two cables connect the target selector to the mount and the mount to the electrical power source.

Operation is almost entirely automatic. Once a gun is emplaced the radar operator causes a radar scanner to continually rotate. When planes appear on the picture tube the operator depresses a dead man foot pedal which stops the rotation of the radar scanner. After making minute adjustments in range, azimuth and elevation, he releases the foot pedal for automatic operation. Automatically the radar tracks the target, feeding data to the computer. The computer plots the future position and aims the gun at this future position. As a target comes within gun range, either the computer or radar operator squeezes the firing trigger and the gun continues to fire automatically.

Due to the complexity of this unit, a 37-week training course for maintenance personnel has been established at the Ordnance School, Aberdeen, Maryland.

Development and production were commenced by Army Ordnance on this weapon late in World War II. The need for such a weapon was determined by the limitations of the 40mm gun in providing defense against high speed, medium altitude aircraft. Once the military characteristics were determined, Ordnance instituted a complete research, development and production program embodying both American industry and our Ordnance arsenals. Included among these are:

The Watertown Arsenal, which serves as project coordinator and technical supervisor; the Sperry Gyroscope Company; the A. C. Spark Plug Division of General Motors; the Acme Standard Engineering Company; Franklin Institute; American Machine and Foundry Company; the Wheland Company; National Forge and Ordnance Company; the Cameron Iron Works and the Frankford, Rock Island and Watervliet Arsenals.