The first Chinese combat aircraft built specifically for aircraft carrier use, the J-15, appears to have been equipped with the in-air refueling pod. These pods contain additional fuel and the hose and drogue refueling gear for getting the fuel to other fighters. Thus when a carrier launches four fighters, two can be equipped with the refueling pod and transfer their fuel to the other two, providing those two with more range and time in the air. This reflects the fact that carrier aircraft can carry more weight in the air than they can when taking off.
This refueling system is particularly useful for carriers (like the Chinese one) that use the STOBAR (short take-off but arrested recovery) system that substitutes a “ski jump” flight deck to replace the catapult. The CATOBAR (catapult) system is used by American carriers and allows aircraft to take off carrying more weight (of fuel or weapons) than STOBAR launched aircraft. The U.S. and Russia have such a pod system but it has never been seem on Chinese aircraft before.
The J-15 started mass production in late 2013, a year after some J-15s were seen making touch and go landings on the new carrier Liaoning. After that several J-15s have were seen at navy air bases painted as combat (gray), not development (yellow), aircraft. By the end of 2013 about twenty J-15s had been built for testing. The first five were exclusively for testing while those built after that were apparently intended to become service aircraft once they had all the tweaks and modifications (for problems discovered during testing) applied. This allowed China to get moving with training pilots and deck crews to handle actual carrier operations. This process could take up to a decade in order to create a core of experienced officers and NCOs (petty officers) who can safely and efficiently supervise these inherently very dangerous operations.
It’s long been noted that the J-15 can’t take off from the Liaoning carrying a lot of bombs or anti-ship missiles because of its STOBAR launching system. Ski jump decks are okay for fighters flying air defense missions but not anything requiring heavy loads. In contrast the new Chinese carrier under construction appears to be designed for catapult (flat, not ski jump deck) operations. Moreover, the front wheel of the J-15 is of the type required to handle catapult launches. Meanwhile the Liaoning J-15s can use the refueling pods if they have to carry out some long-range attack mission (with smart bombs or anti-ship missiles).
For most of the last decade China has been developing the J-15, which is a carrier version of the Russian Su-27. There is already a Russian version of this, called the Su-33. Russia refused to sell Su-33s to China, when it was noted that China was making illegal copies of the Su-27 (as the J-11) and did not want to place a big order for Su-33s but only wanted two, for "evaluation." China eventually got a Su-33 from Ukraine in 2001, which inherited some when the Soviet Union dissolved in 1991.
The first prototypes of the J-15 were under construction for two years, and the aircraft made its first flight in 2010. The Russians were not happy with this development. Russian aviation experts openly derided the J-15, casting doubt on the ability of Chinese engineers to replicate key features of the Su-33. That remains to be seen, as the Chinese have screwed up copying Russian military tech in the past. But the Chinese have a lot of experience stealing foreign technology, so the J-15 may well turn out to be at least as good as the Su-33. China openly boasts of the J-15 being the equivalent of the 30 ton American F-18E. That remains to be seen, and right now the 33 ton J-15 seems more like the earlier 23 ton F-18A (a similar looking but quite different design from the F-18E).
Meanwhile, Russia itself has stopped using the Su-33 in favor of the cheaper MiG-29K (which is also being used by India). The 33 ton Su-33 and the 21 ton MiG-29K were both designed were to operate from the three 65,000 ton Kuznetsovs the Soviet Union was building in the 1980s. But when the Cold War ended in 1991, only the Kuznetsov was near completion. The second ship in the class, the Varyag, was sold to China and was rebuilt as the Liaoning. The smaller Gorshkov was rebuilt and sold to India (who believed the smaller MiG-29K was more suitable for this carrier). The Russians still use the Kuznetsov, which has never undergone refurbishment.