The ESEE 5 was built for one scenario: a pilot on the ground, alone, with only what's strapped to the vest. ESEE Knives designed it to a brief from military SERE instructors, and it shows in every dimension. It runs a 5.25 inch drop point on quarter inch 1095, 11 inches overall and about 16 ounces. It's the heaviest knife in the numbered line, and the most likely to survive whatever gets done to it.
Quarter inch stock is twice the spine of the ESEE 3, and that changes what the knife is for. You can drive it through seasoned hardwood with a baton, pry open a jammed hatch, or use it to dig without worrying about the tip. It slices less finely than its thinner siblings, and on purpose. A downed pilot needs a knife that can't fail, not one that cuts tomatoes cleanly. The ESEE 5P is the plain edge, the 5S adds partial serrations for harness webbing and cordage, and contoured 3D handles in G-10 and canvas Micarta fill the hand for long sessions. It started out as the RAT 5 and belongs with the toughest fixed blade knives made.
Two features set the ESEE 5 apart from the rest of the lineup, and both come straight from the SERE brief. A divot in the handle scale works as the bearing block for a bow drill, so the knife holds the spindle while you make fire by friction. The extended tang past the handle doubles as a glass breaker for a canopy or vehicle window, without putting the edge anywhere near the glass. The longer handle also gives you more leverage when batoning and prying than the shorter numbered knives can.
The ESEE 5 rides in Kydex instead of the molded sheaths of the smaller models, and a spare ESEE 5 Kydex sheath comes with its clip plate included. The 5/6 accessory pouch in black or olive drab rides alongside it, so small survival gear stays with the knife instead of buried in a pack. The 5/6 clip plate and other spares are in ESEE accessories. If you need more reach for camp chores rather than extraction, the ESEE 6 stretches the blade to 6.5 inches on thinner stock.