Developed in conjunction with Italy’s Special Forces, Extrema Ratio’s Ultramarine was designed to provide a single tool for dive operations. It features a blade made of Cobalt Steel N690 and a handle crafted from Polyamide. There is also an EOD variant with Titanium components that have a negligible magnetic mass.

Extrema Ratio decided to adopt a renewable protective film called Lubra-Skin which was developed specifically for them. This silicon spray is easily applied to all disassembled steel parts and creates a waterproof protective film to prevent salt water from adhering to the metal and causing oxidation. Since it is a spray, it can be easily reapplied during regular knife maintenance.

The Ultramarine was designed for five primary functions (prioritized by frequency of use in each function); Field Operations, Underwater Operations, Use as an Emergency Tool, Survival, and Combat. Based on these parameters, individual features were refined.

The retention lanyard allows the user to work on equipment without having to sheath the knife. Additionally, the handle was designed with a plus sized grip and incorporates a special anti-slip material developed by Extrema Ratio to facilitate retention while wearing neoprene gloves.

The knife’s blade includes a specialized net and line cutting system for use in entanglement emergencies. The knife is designed with reduced hilt guards to reduce the chance of entanglement and snaring while in use and the pointed tang was developed as a glass break device. Additionally, besides being a good all around camp knife, the Ultramarine was designed so the handle could be disassembled, the blade attached to a pole, and used as a spear. The blade also features a matte finish to reduce light reflection wile operating in hostile environments.

The Ultramarine was conceived as a multi use, amphibian knife. As such it needs to rapidly and easily transition from the operators waterborne equipment to his field tactical gear. To meet this requirement Extrema Ratio developed two separate sheaths. The dive sheath is a rigid sheath made of ABS plastic which can be worn on the ankle or mounted to equipment webbing with a TEK-LOK fastener. There is also an optional field sheath that is PALS compatible and can be attached to a variety of field and tactical equipment.

The dive sheath is a work of art and is designed to be sleek and hydrodynamic, with a close, tight fit to the body to reduce the risk of entanglements. The sheath also has a quick-release function that allows the knife to be rapidly drawn by simply pulling on the upper portion of the protective flap. The O-ring and retention system are disabled with a strong pull so in a panic or shock situation the user will have access to the knife. The protective flap uses special anti-wet snap fasteners designed for water environments. Finally, the sheath incorporates two sharpening diamond sharpening plates; one for the primary blade and the second for the net cutter.

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