Ozawa's "Northern Force" comprised four aircraft carriers, two World War I battleships partially converted to carriers , three light cruisers , and nine destroyers. His force had only 108 aircraft. (That is slightly more than maximum capacity of the flagship Zuikaku. Ozawa's force was not located until 16:40 on 24 October, largely because Sherman's TG 38.3—which was the northernmost of Halsey's groups—was responsible for searches in this sector. The force that Halsey was taking north with him—three groups of Mitscher's TF 38—was overwhelmingly stronger than the Japanese Northern Force. Between them, these groups had five large fleet carriers , five light carriers , six modern battleships , eight cruisers , and more than 40 destroyers. The air groups of the ten U.S. carriers present contained 600-1,000 aircraft. At 02:40 on 25 October, Halsey detached TF 34, built around the 3rd Fleet's six battleships and commanded by Vice Admiral Willis "Ching" Lee. As dawn approached, the ships of Task Force 34 drew ahead of the carrier groups. Halsey intended Mitscher to make air strikes followed by the heavy gunfire of Lee's battleships.
Question: How many ships comprised Ozawa's "Northern Force"?
Answer: 18