The Y-wing is a heavy fighter/bomber developed during the Clone Wars, and still used by the Rebel Alliance during the Galactic Civil War. The Y-wing is well shielded and carries a sizable proton torpedo payload as well as a turreted ion cannon for disabling enemy vehicles, in addition to standard dual laser cannons mounted in front.
The original configuration had a crew of two, pilot and gunner. By the Civil War era, many Alliance vessels were single-seaters, but two-seater versions were still extant, e.g. the one flown by Princess Leia and C-3PO in Splinter of the Minds Eye.
The Y-wing requires a lot of maintenance to keep functioning at peak performance. Alliance technicians often leave the armor plating removed to reduce maintenance time. The Y-wing's ion cannon turret is notoriously fragile and often left non-functional. For example, out of all the Y-wings involved in the Battle of Yavin only two had functioning ion cannons, one of which was the only Y-wing to survive.
In Rogue One, a pair of Y-wings disabled an Imperial Star Destroyer with a torpedo attack. The torpedoes were apparently special anti-ship weapons that used ion bursts to overload the target's systems, much like an electromagnetic pulse. The attack occurred during a fleet battle over Scarif, so it's not clear whether the Y-wings succeeded on their own or were successful because the ISD was also under fire from Rebel capital ships.