1.1"/75 Caliber Machine Cannon

1.1"/75 Calibre Machine Cannon (Mk 2, Mods 1 & 2)
SPECIFICATIONS Year of Construction: 1929 Date in Service: 1936 Bore: 1.1"/75 Calibre Weight of gun: 12,000 pounds Barrel Weight (each): 556 pounds Elevation: -15/+110 degrees Elevation Rate: 24 degrees/second Wt. of projectile: 0.917 lbs Wt. of complete round: 1.9 lbs Gun length: 119.6 inches Bore length: 82 inches. Grooves and twist rate unknown. Range at 10 degrees: 5,300 yards, 20 degrees: 6,600 yards Max. Range: 7,400 yards @ 40 degrees elevation Muzzle Velocity: 2,700 feet/second Ceiling: 19,000 feet Rate of Fire: 150 rounds/min per tube. Ammunition Types: HE, non-self-destructing. Magazine: Clip fed, seven-round clips. Crew: 9	Photograph of two 1.1"/75 Caliber cartridges. The one on the left is intact. On the right the point-detonating nose fuze has been removed and the tracer element is visible in the base of the projectile. Courtesy of John Lowrence of the USS Greenwood (DE679)
Crew of the Francis M. Robinson (DE-220) manning the Quad 1.1" Machine Cannon. National Archives #80-G-303517
Originally, the Buckley class design specifications called for the Mk 1 40mm Bofors twin-barrel cannon. Due to shortages of this gun (almost the entire production capacity was being installed on the Fletcher class DDs) almost all early Buckleys received the antiquated water-cooled Mk 2 1.1"/75 Caliber Quad-barrel machine cannon. This gun was plagued with a variety of design problems and was universally despised for its lack of reliability, difficult maintenance procedures, and over-complexity. The HE ammunition had a simple impact fuze containing a short time-delay. Theoretically, this allowed it to penetrate an aircraft's skin before detonating. There were no inherent safety mechanisms on the fuzes which were armed upon firing, called "setback" arming. Upon firing, a spring loaded plunger was "setback" by acceleration forces, unlocking the firing pin, which was aligned with the detonator. No further arming was required. Upon leaving the barrel the fuzes were sensitive enough to be prematurely triggered by raindrops or sea spray. Adding to the dangers, the "setback" arming feature could be activated by dropping the projectile clip, which resulted in a fully armed projectile entering the chamber. Upon firing, these fully-armed projectiles detonated in the chamber or barrel, causing significant damage. An individual Gun is a Mk 1. Mk 1s with a flash hider screwed onto the end of the barrel is a Mk 1, Mod 1. Four Mk 1s mounted horizontally comprise a Mk 2. Crews of the quadruple Mk 2 called them "Chicago Pianos".
Contributed by Mr. Samuel Saylor, President of the Destroyer Escort Historical Foundation. Dear Bill, I have enclosed some information about the "notorious" anti-aircraft weapon known as the 1.1". Only a United States Government Committee could have come up with this design. The enclosed article states that Forces in the Pacific were re-armed with Bofors twin and quad 40mm mounts as the weapons became available. They never became available to my ship, *USS Connolly, DE-306. For over two years I suffered with a weapon that you could never be sure of what it would do. On Christmas Eve, 1944, while in convoy, that gun took off firing and spent 64 rounds before it stopped. To this day no one knows why or how it did what it did. I was called to the bridge and asked by our Captain, "what happened?" The only reply I could think of was, "Captain, I think it just got the Christmas Spirit." Needless to say that did not go over very well. In all fairness, we fired thousands of rounds and it was a very important segment of our AA defenses. The biggest headache was maintaining it. All in all, I would say it had a mind of its own. The explosion of number three gun barrel (click on the picture above to see a larger image) took place while firing at mines off Guadalcanal in the Solomon Islands. It wounded four of my gun crew. There are 11 men on a gun crew. An inquiry determined that w e had received a lot of faulty ammunition. We carried a spare barrel and by working through the day and evening we were able to replace the damaged one. Three of the wounded stayed aboard while the fourth was placed aboard a hospital ship the next day. He lost his right knee cap. When we test-fired the new barrel, only the Gunnery Officer, Chief Gunner's Mate and I were present. All went well and there were no more muzzle bursts. We de-commissioned in Charleston, SC and I had the great pleasure of assisting in removing the 1.1" from the ship and driving the truck to the scrap pile. I think I said "Hey gun, at last, I got you." As I told you on the phone, there is a 1.1" in Liberty park, Omaha, Nebraska and one aboard the USS Yorktown*, at Patriot Point, Charleston, SC. I hope this gives you a bit of knowledge about this infamous weapon.
A gun crew receiving instruction at Dam Neck, Virginia on 3 August 1942. Note the other gun mounts further down the firing line. There appear to be two 20mm guns and, furthest away, two 3"/50 calibre mounts. National Archives #80-G-10275
A gun crew receiving instruction at Dam Neck, Virginia on 3 August 1942. This is the same group as above, but the stack of 7-round clips piled behind the mount is visible. National Archives #80-G-10280
A 1.1" crew aboard ship in April 1942. National Archives #80-G-07134
A 1.1" crew aboard ship in April 1944. National Archives #80-G-19696