Navy SEALs require knives capable of cutting wet rope, withstanding saltwater corrosion, and operating reliably in sand and mud. Since 1982, the Mark 3 Mod 0 has served as the standard issue knife. While SEALs today can select their own knives, the requirements remain specific: they must perform cutting tasks, support survival needs, and function in combat while maintaining their edge and structure in marine environments.
The Mark 3 Mod 0: Standard Issue Since 1982
The Pritzker Military Museum and Library confirms that the Mark 3 Mod 0 knife became the standard issue fighting utility knife for Navy SEALs in late 1982. This knife replaced the Mark 2, which had served naval forces but lacked the specific features needed for underwater maritime operations.
The Navy had previously issued its MK 1 Deck Knife as a utility blade since the 1940s, according to The Armory Life. Neither of these earlier knives could meet the demands of undersea warfare and amphibious operations that SEALs faced.
The Mark 3 represented a purpose-driven approach to knife design for maritime warfare. The Armory Life reports that preliminary knives went to Naval personnel, particularly SEALs, for testing and evaluation in 1980. Two years of field testing confirmed that this knife could withstand the punishing conditions SEALs encountered during operations.
Blade Specifications and Materials
The Mark 3 features a six-inch blade made from 440A stainless steel. This steel has a hardness rating of 49-54 HRC, which is a milder stainless steel suitable for diving and survival applications. The 440 series steel contains at least 10.5% chromium, providing the corrosion resistance essential for maritime operations. The 400 series remains popular among knife makers because it sharpens easily and resists corrosion effectively.
The blade design uses a low, flat grind with a clip point. The sawback feature cuts through wet rope or webbing, which SEALs encounter frequently. Black Scout Survival confirms that the saw-tooth back, combined with a black oxide finish, protects the blade from rust and reduces light reflection during covert operations.
Handle Design and Construction
The Mark 3’s handle is black, high-impact, molded plastic with a checkered grip pattern and USN markings in the center. This thermoplastic material provides a solid grip when wet or when operators wear gloves.
SlashGear provides additional technical details about the glass-filled polyamide handle construction. This material offers electrical insulation and shock resistance, with an isolated steel pommel that serves as a hammer. The handle maintains its grip and structural properties in wet conditions, which is essential for amphibious operations.
Sheath System and Carry Options
The Mark 3’s sheath incorporates several features designed for maritime operations. Black Scout Survival explains that the sheath locks the knife via a pressure-spring mechanism. This system keeps the knife secure without requiring the handle strap to be snapped closed, preventing knives from falling into the ocean during underwater operations. The design saves the Navy money by reducing equipment loss while providing operators with quick access to their blade.
Users can attach the knife to web gear using a brass hanger or wear it on a belt loop. The sheath includes a leg tie-down strap, a standard for dive-purpose knives. This configuration allows SEALs to position the knife for quick access, preventing it from floating or shifting underwater.
Alternative Knives Used by SEALs
While the Mark 3 remains the official issue, Black Scout Survival confirms that SEALs may carry personally purchased blades at their discretion. The Armory Life supports this, stating that modern SEALs are free to select their own knives. As of 2025, it remains unclear whether the Mark 3 was officially replaced or whether Navy SEALs were granted permission to choose their own blades.
The SOG SEAL Pup is another knife issued to SEALs. This shorter and lighter knife carries a U.S. National Stock Number, lending credibility to its military use. It’s a fixed blade with an AUS-8 blade, a Japanese stainless steel that balances edge retention with corrosion resistance.
Material Requirements for SEAL Knives
SEALs require knives built from materials that withstand marine environments. Stainless steel is ideal for combat and field use because it needs less maintenance than carbon steel. The material must resist saltwater corrosion while maintaining its edge through extended use. SEALs prioritize material robustness when selecting knives.
G-10 has become a preferred handle material for tactical knives used by special operations forces. Wikipedia describes G-10 as having high strength, low moisture absorption, and chemical resistance. It scales well for military and rescue scenarios due to its chemical resistance and durability. The material’s textured surface provides grip security even when wet. G-10 maintains its shape and form better than wood, never warping or changing over time.
Blade Features for Operational Requirements
SEALs need knives that handle multiple tasks during operations. Their blades must cut ropes, serve as self-defense tools, support survival tasks, maintain equipment, and prepare food in field conditions. Tactical knife resources indicate that blade lengths between four and seven inches provide optimal balance for combat and survival situations. The Mark 3’s six-inch blade falls within this range, offering sufficient length for various applications without becoming cumbersome.
Serrated edges prove valuable for specific SEAL applications. Data from emergency response teams shows that serrated edges excel at cutting materials that obstruct rescue operations. Controlled cutting tests demonstrate that serrated blades outperform plain edges on webbing and thick fabric.
Serrated tactical knives work effectively on rope, webbing, fibrous materials, and packaging. Serration mechanics create focused penetration points at each tooth’s acute edge, while concave grooves provide multiple cutting angles that automatically conform to the material being cut.
Modern Considerations for SEAL Knives
SEALs operating in 2025 face varied mission profiles that demand versatile cutting tools. Urban operations require compact blades that can be concealed yet remain accessible. Maritime missions still demand corrosion-resistant materials and secure retention systems. Desert deployments need knives that resist sand infiltration while maintaining their mechanical function.
At Urban EDC, we produce tactical knives that incorporate lessons learned from military knife development. Our fixed blade designs feature corrosion-resistant steel alloys and textured handle materials that maintain grip in wet conditions. Our knives use the same principles that have made the Mark 3 effective: appropriate blade length, durable construction, and retention systems that help prevent loss during demanding use.
Training and Knife Skills at BUD/S
Black Scout Survival confirms that the Mk 3 MOD 0 Diving Survival knife serves as the issued knife during Basic Underwater Demolition/SEAL training. Trainees learn knife handling, maintenance, and deployment techniques using this standard blade. They practice cutting techniques on various materials they might encounter during operations, including paracord, seat belts, and fishing nets.
The training emphasizes knife retention as much as knife use. Losing equipment underwater creates operational hazards and compromises missions. The Mark 3’s sheath design, with its pressure-spring retention system, becomes part of muscle memory during repeated training evolutions. Operators learn to verify knife security before entering the water and to check retention systems after exiting.
The Evolution from Earlier Navy Knives
The transition from the Mark 1 and Mark 2 knives to the Mark 3 represented a shift in naval special operations philosophy. Earlier knives served general utility purposes aboard ships. The Mark 3 addressed specific requirements arising from SEAL combat swimming, beach reconnaissance, and direct-action missions. The Armory Life describes the Mark 3 as the first Navy knife designed as a “purpose-driven bladed tool” specifically for underwater operations.
This evolution continues as SEALs adapt their equipment selections to match changing operational environments. Personal knife selection allows operators to choose blades that match their specific mission sets while meeting baseline requirements for durability and functionality.
Maintenance and Care Requirements
The 440A stainless steel used in the Mark 3 requires less maintenance than carbon steel alternatives, but SEALs still follow strict care protocols. Regular cleaning removes salt deposits that can cause pitting even in stainless steel. The black oxide coating needs periodic inspection for wear that might expose bare metal to corrosion.
Handle materials like the Mark 3’s thermoplastic or modern G-10 composites resist degradation but still require cleaning to maintain grip texture. Sand and salt crystals can accumulate in checkering patterns, reducing grip effectiveness. SEALs learn to completely disassemble and clean their knives, ensuring reliable function when needed.
Final Thoughts on SEAL Knife Selection
The Mark 3 Mod 0 remains the benchmark for SEAL knives 40 years after its adoption. Its six-inch 440A stainless steel blade, thermoplastic handle, and secure sheath system established standards that modern tactical knives still follow. While SEALs now select from various personally purchased options, their knives must meet the following requirements: corrosion resistance, edge retention, secure grip, and reliable retention systems.
Our tactical knife designs incorporate these proven features, providing both civilians and professionals with blades built on principles tested in challenging environments. The Mark 3’s legacy is reflected in modern knives that balance cutting performance, durability, and practical carry options for users who need reliable tools.