The $21-million cost of sinking the decommissioned Navy attack aircraft carrier USS Oriskany -- called the "Mighty O'' -- was cheaper than scrapping it, according to Navy estimates. And the carrier's role as an artificial reef -- 212 feet underwater some 23 miles southeast of Pensacola Pass -- should make it a valuable magnet for sea life, divers and sports fishermen. The 888-foot, 32,000-ton vessel served from 1946 to 1976 and saw combat in the Korean and Vietnam wars and is the first carrier deployed as a reef.