Description
Inert 20mm Mark 4 Brass Cartridge Case for the 20x110mm Oerlikon Cannon
Item Overview
This inert 20mm Mark 4 brass cartridge case represents the fixed ammunition used with the Oerlikon antiaircraft cannon. Its heavy brass construction and rebated-rim design make it an identifiable example of the 20x110mm Oerlikon ammunition family. This case is completely inert and intended for collecting, historical study, restoration projects, museum exhibits, or display. It does not include a projectile or any live ammunition components.
Identification and Features
U.S. Navy manuals list the Mark 4 as the brass version of the service cartridge case used with the 20mm Oerlikon antiaircraft gun. The related Mark 3 case was made from steel. Both were designed for the same ammunition family and could be assembled with several types of 20mm Oerlikon projectiles. The Mark 4 cartridge-case designation is separate from the Mark and Mod numbers assigned to Oerlikon gun mounts.
- Item: Empty cartridge case
- Designation: Mark 4
- Caliber: 20mm
- Ammunition family: 20x110mm Oerlikon, also known as 20x110mm RB
- Material: Brass
- Associated weapon: 20mm Oerlikon antiaircraft cannon
- Original ammunition type: Fixed ammunition
- Historical primer specification: Mark 34
- Historical empty-case weight: Approximately .190 lb.
- Offered condition: Completely inert display component
- Included: One inert Mark 4 brass case
- Not included: Projectile, propellant, live primer, ammunition container, gun, or display stand
Rebated-Rim Case Design
The 20x110mm Oerlikon cartridge is commonly described as 20x110mm RB. The letters RB stand for rebated rim, meaning the rim at the base is smaller than the widest part of the case body. This distinctive feature helped the case work with the Oerlikon cannon’s operating and extraction system. The 20mm figure identifies the projectile diameter, while 110mm describes the approximate case length. Oerlikon ammunition should not be confused with 20x110mm Hispano ammunition, which shared the same nominal caliber and case length but used a different case and rim design.
Original Service Function
In a complete service cartridge, the brass case held the primer and propellant charge while supporting the projectile at its mouth. The assembled cartridge was loaded into the gun as one unit. When fired, the case expanded against the chamber walls and helped prevent propellant gases from escaping through the breech. After the projectile left the barrel, the empty case was extracted and ejected as the gun continued its operating cycle. This information describes the original military function; the case offered here contains no live primer, propellant, projectile, or other energetic material.
Ammunition Applications
The Mark 4 case could be assembled with different Oerlikon projectiles according to the intended mission. Period ammunition families included high-explosive, high-explosive incendiary, high-explosive tracer, armor-piercing tracer, ball, and practice types. Complete service cartridges used specific projectile, primer, and propellant combinations approved for the weapon. This listing is for the empty inert brass case only and does not identify it as a complete example of any one loaded ammunition type.
History of the Oerlikon Cannon
The Oerlikon cannon developed from Swiss automatic-cannon designs. The U.S. Navy tested early Oerlikon weapons in 1935 but did not adopt them at that time. The growing threat from dive bombers and other low-flying aircraft later created a need for a reliable short-range naval gun. After studying an improved Oerlikon design and British wartime experience, the Navy approved the weapon for service in November 1940. American production expanded quickly as the United States prepared its ships for World War II.
Naval Service and Wartime Use
During World War II, Oerlikon guns were installed aboard aircraft carriers, battleships, cruisers, destroyers, escort vessels, landing craft, patrol boats, and armed merchant ships. The gun was normally served by a small crew and fed from a removable drum magazine. It provided rapid close-range fire against aircraft that passed through longer-range antiaircraft defenses. Oerlikon guns also could be used against small boats and exposed targets. Millions of cartridges were required for combat operations, crew training, shipboard readiness, and replacement stocks.
Training and Gun-Crew Operation
Oerlikon crews trained to recognize targets, track aircraft, fire controlled bursts, replace magazines, clear stoppages, and maintain the weapon in harsh conditions at sea. The gunner aimed and fired while other crew members supplied loaded magazines and removed empty ones. Regular practice was important because low-flying aircraft approached quickly and left little time to respond. Fired Mark 4 cases were ejected during this cycle, making surviving brass cases direct reminders of the weapon’s operation and the teamwork required from its crew.
Condition
This is an inert surplus brass cartridge case that may show scratches, dents, tarnish, oxidation, staining, discoloration, mouth deformation, primer-pocket wear, tool marks, or other evidence of age, firing, handling, storage, and deactivation. Headstamps, dates, manufacturer markings, finish, and minor details may vary among available examples. This listing does not claim a particular manufacturer, production date, or fired condition unless specifically shown or stated. Please review the inventory photographs for the item’s general condition.
Ideal For
This Mark 4 brass case is well suited for displays covering World War II naval weapons, Oerlikon cannons, fixed ammunition, and U.S. Navy antiaircraft defense. It can be displayed alone or paired with period manuals, photographs, and other inert components to explain how a complete Oerlikon cartridge was constructed.
- 20mm Oerlikon ammunition collections
- World War II naval displays
- Inert cartridge-case collections
- U.S. Navy antiaircraft exhibits
- Military museums and educational programs
- Restoration and reference projects
- Gun-room and military-history displays
Approx length 4", Approx width .87", Approx height .87", Approx weight .19 lbs.
Pictures are stock images of our inventory. Unless otherwise noted, you will not be receiving the exact item shown in the pictures. The pictures are representative of the item’s general condition. The item you receive might be slightly better, or worse, condition than was shown in the pictures.
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