Tuesday, September 23, 2014

12th AAA War Diary : September 23, 1944 - Radar, searchlights and 90MM guns unloaded

The HAA Group was Daddy's main unit.  He was part of Battery "C" as a Fire Control Man.

Below are some photos and setups of the radar systems mentioned in the entry above used by the 12th :

The SCR-268 radar, seen from the back, or control, position, showing the azimuth receiving array at left, the elevation receiving array at right, and the transmitting array in the center. Bottom: artist's illusration of a typical searchlight and SCR-268 setup, including transport vehicles. AAA guns would be sited further away, but would be connected to the light, radar, and controller units with cables.

SCR-268 radar emplacement on Guadalcanal 1942

The SCR-268 was considered a searchlight radar ; a short-range, height-finding unit expressly designed for fixed antiaircraft defenses such as coastal batteries or other static positions. The method for using the SCR-268 would be to use it to pick up the airplanes at night and to synchronize the radar plot with a searchlight through an already developed gun director. The director performed the basic mathematical function of taking the range and angle data out of the radar and aimed the searchlight in that direction. At the appropriate moment, when range and angle to target were known, the controller would order the searchlight turned on. At that moment, the target was illuminated and it could be engaged by guns. A side benefit was that the pilot would be blinded. It was also advantageous to wait as long as possible to turn on the light since the longer the beam remained on, the more vulnerable the light and crew was to retaliatory fire.

PFC Homer Amay, USMC, of Williamsport, Pennsylvania, adjusts the detector controls on a 60-inch searchlight during training at the Marine Ordnance School, Quantico, Virginia on August 13, 1942.
A restored General Electric searchlight from the wartime era in California; (left to right) the restored light, control station, and generator.
The crew of a 90mm gun stands by for action in the Solomons during November 1943.

This 3rd Defense Battalion 90mm antiaircraft gun, dug in at Guadalcanal, served in a dual role with its ability to engage targets on the ground as well as in the air.

The 90mm antiaircraft guns on Rendova, as this one, threw up a barrier of fire to protect the troops attacking Munda airfield from enemy air raids and, in doing so, showered shell fragments on the Marines across New Georgia at Rice Anchorage.
Typically, each 90mm AAA Gun Battallion consisted of a Headquarters and HQ Battery, and four firing Batteries, A to D. Each firing battery had four towed 90mm guns plus fire direction equipment.

The 90mm AAA had an altitude capability of 30,000 feet and a range of 14 miles, firing a 24 pound shell. The ammunition was improved dramatically when fitted with VT proximity fuses at the end of 1944. The 90mm gun was very effective and was credited with downing many enemy aircraft during World War II.  A single 90mm gun could put 20 to 28 rounds in the air every minute -- a battery of four guns was devastating when on a single target. A crew of 8 to 10 was required to operate and maintain the 90mm gun, including the section chief, loader, gunner, azimuth pointer, elevation pointer and an ammo section.

The 90mm gun section was commanded by a sergeant, designated as the section chief. A corporal served as the gunner, and also commanded the gun squad. One Marine was responsible for traversing the gun, and another for elevating and depressing it. A corporal and four Marines were assigned to the ammunition squad. Finally, a driver was assigned to the section. The gun was towed by a 2 & 1/2 ton truck, or sometimes by a bulldozer for short distances.
The battery was usually aimed and fired at as a coordinated unit against aerial targets. Battery headquarters was connected by field phones to the guns, and the fire direction center telephoned deflection, elevation, and time of flight out to the gun sections. The headquarters' director squad gathered data on the incoming targets's direction, altitude and speed, and then fed this data into the director set, which was a simple computer that estimated elevation and deflection for the guns, as well as flight time in seconds to the target. Information on the enemy's location usually came via radar, typically the SCR-268 search radar. In an emergency, the direction squad could could the enemy's speed, range and altitude by visual estimation. Upon receiving the data, crews set their guns, and fired at the coordinates, usually in massed fire at a single target.