Description
20mm Mark 3 Projectile for the 20x110mm Oerlikon Cannon
Item Overview
This 20mm Mark 3 projectile represents an important family of ammunition used with U.S. Navy 20x110mm Oerlikon antiaircraft guns. The Mark 3 was produced in high-explosive, high-explosive incendiary, and blind-loaded practice configurations. Each type used the same basic steel projectile body but carried a different internal filling and identifying color. This listing is for one projectile component only and does not include a cartridge case, primer, propellant charge, magazine, or weapon unless specifically stated.
Identification and Features
U.S. Navy manuals identify the complete family as the 20mm antiaircraft H.E., H.E.-I., and B.L. & P. Mark 3, Mods 1 through 64. The numerous Mod numbers were used mainly to identify products made under different contracts. The Mark and Mod designation, manufacturer’s symbol, and lot number were normally stamped into the projectile body. Exact markings, paint, nose components, and internal condition may vary among surviving examples.
- Designation: 20mm Projectile Mark 3
- Modification range: Mark 3 Mods 1 through 64
- Documented service types: High-explosive, high-explosive incendiary, and blind-loaded and plugged
- Cartridge family: 20x110mm RB Oerlikon
- Original service fuze: Mark 26 Mod 0 or Mark 26 Mod 1 nose fuze
- Tracer: Not used in the standard Mark 3 configurations
- Documented length with fuze: Approximately 3.275 inches
- Documented length without fuze: Approximately 2.625 inches
- Documented loaded weight: Approximately 0.2714 pound
- Offered component: One projectile only
- Current inert status: Not confirmed by the information provided
Documented Mark 3 Configurations
The standard H.E. Mark 3 contained approximately 0.0243 pound of tetryl or pentolite. The H.E.-I. version combined approximately 0.0072 pound of incendiary mixture with approximately 0.0171 pound of tetryl or pentolite. The projectile was also issued as B.L. & P., meaning blind-loaded and plugged. That practice configuration used an inert filler and a dummy nose cap in place of the service explosive filling and fuze. The model name alone does not identify which configuration this particular projectile represents.
Original Service Function
The live H.E. projectile was designed to burst when its Mark 26 nose fuze functioned against a target. The H.E.-I. type added an incendiary mixture intended to help ignite fuel, fabric, and other vulnerable aircraft materials. The blind-loaded practice version gave gun crews an inert projectile body for training without a high-explosive charge. A copper-alloy rotating band near the base engaged the barrel rifling, sealed the propellant gases, and gave the projectile the spin needed for stable flight.
Construction and Service Specifications
The Mark 3 had a documented base diameter of approximately 0.74 inch and a maximum bourrelet diameter of approximately 0.78 inch. Its rotating band was approximately 0.16 inch wide and was positioned about 0.374 inch from the base. The loaded service projectile weighed approximately 0.2714 pound. These measurements describe the original military assembly, so an empty projectile body, missing fuze, replacement plug, or removed filling can change the length and weight of a surviving example.
Markings and Wartime Colors
Period U.S. Navy instructions used color to separate Mark 3 loadings. An H.E. projectile filled with tetryl was painted white, while one filled with pentolite was painted yellow. H.E.-I. projectiles were red for tetryl or light pink for pentolite. The blind-loaded and plugged version was dark gray-green. Surviving projectiles may have faded, repainted, or removed finishes, so color should be compared with stamped markings and internal construction before assigning an exact type.
Cartridge and Weapon Application
The Mark 3 projectile was loaded into fixed 20x110mm RB Oerlikon ammunition. The reduced or rebated rim of the cartridge case helped distinguish Oerlikon ammunition from the separate 20x110mm Hispano family. Navy manuals list the Mark 2 cartridge case for the H.E. loading and Mark 2, Mark 3, or Mark 4 cases for the H.E.-I. loading. Complete ammunition was used with U.S. Navy 20mm Oerlikon gun mechanisms, including Marks 2 and 4. Oerlikon and Hispano cartridges were not interchangeable despite their similar caliber and overall appearance.
History of the 20mm Oerlikon Gun
The Oerlikon cannon was developed in Switzerland from an earlier automatic-cannon design. U.S. Navy manuals described the Mark 1 as the original Swiss gun and the Mark 2 as an improved version made in Britain and the United States. The American Mark 4 gun was almost identical to the Mark 2 but used different manufacturing limits. Its simple action, drum magazine, and compact pedestal mount allowed the weapon to be installed on vessels ranging from small patrol boats and landing craft to large aircraft carriers and battleships.
History of Use
During World War II, 20mm Oerlikon guns became a common part of Allied shipboard air defense. Crews used them against low-flying bombers, torpedo aircraft, and strafing attacks in the Atlantic, Mediterranean, and Pacific. The guns protected convoys, amphibious forces, merchant vessels, and major fleet units. They were especially valuable when an aircraft entered the close defensive area around a ship. Mark 3 high-explosive and high-explosive incendiary projectiles gave these gun crews ammunition designed to damage aircraft structures, engines, fuel systems, and control surfaces.
Historical Significance
The Mark 3 projectile represents the early explosive ammunition used by one of the most widely installed Allied naval antiaircraft guns of World War II. It also shows how one projectile design could be adapted for explosive, incendiary, and practice roles. Its markings, remaining paint, nose arrangement, and rotating band can provide useful information about wartime production and the development of close-range naval air defense.
Condition and Safety Status
This is a surplus projectile component that may show scratches, oxidation, pitting, dents, paint loss, discoloration, tool marks, or other signs of age and storage. The supplied information does not confirm whether the projectile cavity and nose components are empty. This description therefore does not certify the offered item as inert. Because live Mark 3 projectiles contained energetic material, the item must be professionally inspected before it is advertised or handled as inert. Age, missing paint, or the absence of a cartridge case does not prove that a projectile is safe.
Ideal For
Once its inert condition has been properly verified, this Mark 3 projectile can serve as a strong display piece for collections covering U.S. Navy ammunition, automatic cannons, and World War II shipboard air defense.
- 20mm Oerlikon ammunition collections
- World War II naval displays
- U.S. Navy ordnance exhibits
- Automatic-cannon ammunition studies
- Military museums and educational collections
- Projectile identification and restoration projects
Approx length 3.275", Approx width .78", Approx height .78", Approx weight .27 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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