Ocean explorer Bob Ballard tapped to find downed Turkish warplane Syria maintains the plane was within its airspace when it was shot down June 22, but Turkey disputes that. Territorial airspace extends 12 nautical miles offshore. Debris, if found, could help settle the matter. If the plane was hit by antiaircraft gunfire, it was probably attacked within Syrian airspace, as such weapons have limited range, said a senior U.S. military official who spoke on the condition of anonymity because of the sensitivity of the issue. But if the wreckage indicates that a missile downed the plane, then it could have been hit either in Syrian airspace or farther out to sea. The official said that U.S. intelligence reports have been "in­conclusive" on the location of the plane when it was hit and the type of weapon fired at it. In an interview published in Turkey on Tuesday, Syrian President Bashar al-Assad said he regretted the incident. "We had absolutely no idea about the identity of the plane when we were shooting it down," Assad said. We do not even want to think that this plane was deliberately and purposefully sent into our airspace. We want to think that the pilot made a mistake. Turkey has said the aircraft was on a training mission and briefly and mistakenly entered Syrian airspace. Turkish officials, after asking NATO allies for resources to help with the search, approached the Nautilus team via the U.S. Embassy in Ankara last week. Ballard agreed to take on the mission, delaying a scientific expedition to explore the Black Sea and the eastern Mediterranean. On Friday, the 211-foot Nautilus steamed out of Istanbul toward the Syrian coast, according to a statement from Turkey's Foreign Affairs Ministry. The ship is now "under control of Turkey," with Turkish officials onboard and directing the search, the statement read. Turkish naval ships are escorting the vessel. A Ballard spokeswoman aboard the Nautilus, Liz Smith, said via e-mail that she could not provide details of the effort. With powerful sonar and two remotely operated vehicles (ROVs) onboard, the Nautilus is equipped to find the jet's wreckage, said Charles Royce, a veteran of similar searches as vice president of Oceaneering International, a Houston company that builds undersea remotely operated vehicles. Ballard's search is likely to have started near the last radar contact with the F-4, Royce said. Any such search begins by dropping sonar "towfish" into the water, which trail behind and scan the bottom. Cutting swaths across the search area, the sonar towfish will hunt for a debris field - the same strategy that Ballard employed in the North Atlantic in 1985. There, he hit a historic jackpot: two enormous broken halves of the Titanic.