It was a "durable aircraft and could withstand tremendous damage and still fly" because it was designed and built by the world famous "Grumman Iron Works," a company noted for building hell-for-strong aircraft for the U.S. Navy since before WWII.
The A-6, as are all aircraft destined for service in a U.S. Navy Carrier Air Wing, was specifically designed for that extremely harsh environment, plus the combat environement, of course. All carrier-based aircraft are substantially heavier than aircraft designed only for land operations.
Grumman built fine airplanes for the U.S. Navy, and I am proud to have flown them from 1965 until 1981. We made fun of them, but, damn, they could "take a licking and keep on flying!"
Frank L. Davis, Jr.
Captain, USNR (Ret)
Naval Aviator # V23271