The Ultramarine is the result of 4 years of development by Extrema Ratio in cooperation with military diving teams and special forces. It is also suitable for combat situations in the field, situations such as underwater rescue knife, in emergency situations, as a survival knife or as a tool for special operations. The blade is made specifically for use under water and can withstand high pressure without breaking. On the one side, the blade is straight sharped and is dagger style formed. On the other hand, the blade was designed with a serrated edge and features a shackle opener. The other well thought out feature of this knife is the hole in the middle of the blade, which reduces water resistance.