Constructed of aerospace grade aluminum with a rugged military specification hard-anodized finish, and powered by two lithium batteries (10-year shelf life), the U2 Ultra features a five-watt LED (Light Emitting Diode) and the extended runtime typical of LED flashlights. The U2 features a body-mounted selector ring that allows the user to choose one of six output levels: from a battery saving two lumens of light—perfect for finding your keys in the dark—to a retina-searing 100 lumens at its highest setting. The U2 is equipped with a click-on/off tailcap pushbutton switch that gives the user the option of momentary activation (for self-defense use or emergency signaling) or the convenience of a constant-on “click” switch. The U2 also features microprocessor regulation circuitry to match the LED's current requirements with the battery's output to maintain a more consistent level of light output for the useable life of the batteries (as opposed to unregulated lights, which are subject to a steady decline in light intensity beginning shortly after activation).

The U2 produces over 40 hours of useful light on the lowest setting. Unlike most LED flashlight manufacturers -- who inflate the light output and usable runtimes of their LEDs -- SureFire provides realistic output and runtime specifications based on scientifically obtained measurements. Although any LED -- including those produced by SureFire -- can continue to produce negligible light output for over 100 hours, the amount of useful light produced is of a shorter duration.