The flechette torpedo was a new weapon developed for the Battle of the Corellian Queen. The projectiles were loaded with jagged bits of durasteel packed around a core of conventional explosive. The shells would detonate and in effect become a debris field for incoming TIE Defenders, not equipped with particle shields to defend against material objects.
Not only did the New Republic forces use them to destroy enemy ships, but to track those TIEs which survived the battle. The escaping fighters actually had debris from the flechette torpedoes in their titanium-reinforced hulls, and this debris contained hundreds of thousands of solid-state transponders triggered by a very specific subspace signal. The transponders, conceived by Wedge Antilles, allowed the NRDF to find Lord Shadowspawn's base at Mindor.
At some point, the Imperials managed to replicate the technology, and included them on their TIE/IT Interdictor starfighter line's ordnance.