| Original caption: “View of number four ninety millimeter anti-aircraft artillery gun emplacement with crew in pit. “D” Battery, ninety-eighth Anti-Aircraft Artillery Gun Battalion, 137th Anti-Aircraft Artillery Group Okinawa.” The M1A1 90 millimeter (3.5 inch) anti-aircraft could fire 20 rounds a minute from a fixed emplacement. In anti-aircraft use, the guns were normally operated in groups of 4, controlled by the M7 or M9 gun director or Kerrison predictors. Radar direction was common, starting with the SCR-268 in 1941, which was not accurate enough to directly lay the guns, but provided accurate ranging throughout the engagement. For night-time use, a searchlight was slaved to the radar with a beam width set so that the target would be somewhere in the beam when it was turned on, at which point the engagement continued as in the day. In 1944, the system was upgraded with the addition of the SCR-584 microwave radar, which was accurate to about 0.06 degrees (1 mil) and also provided automatic tracking. With the SCR-584, direction and range information was sent directly to the Bell Labs M3 gun data computer, and M9 director, which could direct and lay the guns automatically, all the crews had to do was load the guns. Note the gun positions being prepared behind number 4; shirtless gun crew working in the Okinawan heat; oil barrels used as protection; sand bags on top of oil barrels. | |
| Image Filename | wwii2155.jpg |
| Image Size | 1.06 MB |
| Image Dimensions | 2904 x 2288 |
| Photographer | |
| Photographer Title | United States Army Signal Corps |
| Caption Author | Written or Adapted by Jason McDonald |
| Date Photographed | July 18, 1945 |
| Location | |
| City | |
| State or Province | Okinawa |
| Country | Ryukyus |
| Archive | National Archives and Records Administration |
| Record Number | NWDNS-111-SC-211476 |
| Status | Caption ©2026 MFA Productions LLC Please Do Not Duplicate or Distribute Without Permission; Image in the Public Domain |
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