Such a battle would primarily involve the navies of both sides. Each operates on a different premise. Japan has a force of destroyers that are highly capable in anti-surface and anti-submarine operations. Japans guided missile destroyers are also highly capable anti-air vessels.
Japan has a total of 30 destroyers, nine guided-missile destroyers, and nine frigates. At least two of the older Tachikaze-class guided-missile destroyers will be replaced by the new Atago-class destroyers. Japan also has 16 modern diesel-electric submarines.
The Chinese navy is larger in numbers carrying 25 destroyers and 45 frigates. However, of these 25 destroyers, 16 are the obsolete Luda class. The same is true for the Chinese frigates two-thirds of them are the obsolete Jianghu-class ships. These are equipped with antiquated HY-2 missiles, which are copies of the old SS-N-2 Styx state of the art for 1960. These days, a Styx is an easy kill for any modern surface-to-air missile. China has 65 diesel-electric submarines, but 52 of them are obsolete Romeo and Ming-class submarines. Chinas Han-class SSNs are also old and noisy. Again, in terms of modern vessels, China is outnumbered.
Another factor is air cover. The disputed waters are within 300 kilometers of Okinawa. This is easily within the combat radius of the Japanese Air Self-Defense Forces F-1, F-4EJ Kai, F-15J, and F-2 fighters. Japan has a major air base in Naha, and there is also Kadena Air Force Base, where the United States Air Force keeps a wing of F-15s. The oldest aircraft in service with Japan are the F-4EJ Kais and F-1s the latter are being replaced by the F-2.
Chinas fighters tend to be very old. The only real modern fighters are the J-11 (Russian Su-27) and the Su-30MKK (an Su-27 variant). Japan is almost at parity in terms of numbers (187 F-15J/DJs and 140 F-2s to 380 J-11/Su-30MKK in Chinese service). Japan has superb pilots as well, who get plenty of training. Chinese pilots get less flying time, although they are increasing their training.
Japan also has E-2 and E-767 airborne early warning aircraft that they have years of practice using, while China has only recently acquired Russian A-50 Mainstays.
In a straight naval-air fight over the Senkaku Islands, Japan has an advantage, even if they are on their own. While China is modernizing, Japan is not standing still, modernizing its military and keeping a qualitative edge over its larger neighbor. Harold C. Hutchison (firstname.lastname@example.org)
Recently, a Chinese surface group was detected by a Japanese P-3C in disputed waters near the Senkaku Islands. The group, which consisted of a Sovremenny-class destroyer, two Jianghu I-class missile frigates, a replenishment ship, and a missile observation support ship, was a reasonably powerful force. It does lead to the question: Who would prevail in a fight with Japan over the Senkaku Islands?