The meridian trench, sometimes called the Polar Trench, was a trench situated near the north pole of the Galactic Empire‘s Death Starbattle station. It contained its only weakness, the thermal exhaust port. After the Alliance to Restore the Republic managed to steal the plans to the Death Star, they discovered that fatal flaw. Consequently, the Alliance decided to send an attack run of starfighters down the meridian trench in order to fire a proton torpedo into the exhaust port, triggering a chain reaction that would cause the Death Star’s main reactor to explode. After navigating his T-65B X-wing starfighter through the meridian trench, Luke Skywalker managed to destroy the battle station as planned.
Did you know the Death Star trench in A New Hope is not the equatorial trench? It’s a common misconception, but the Rebel briefing shows that it starts about halfway up from the equator and heads towards the superweapon’s north pole. According to effects designer Joe Johnston it was one of eighteen similar trenches, and was forty miles long.