One of the most frequently used Russian missiles in Ukraine is the Kh-101. This missile is a stealthy version of the non-stealthy Kh-555, which is an upgraded version of the Kh-55 which entered service in the early 1980s as a Russian version of the American Tomahawk. The KH-101 was part of the Russian post-Cold War catch-up (to the Americans) effort. The Kh-101 was first noted hanging from a Tu95 heavy bomber. The Kh-101 was in development for nearly two decades, but most work was halted in the 1990s because of money shortages. In 2002, there were indications that work had resumed on the Kh-101.
Eventually, Tu-160 and Tu-95MS heavy bombers were equipped to carry a dozen Kh-555 cruise missiles each. These missiles are upgrades (longer range) of the Cold War era Kh-55 nuclear cruise missile. The Kh-555 is 20 feet long, weighs 1.5 tons and has a range of 3,000 kilometers. An 800 pound conventional warhead appears to be a cluster bomb type (carrying bomblets). The missile uses inertial and satellite supplied guidance, and can hit within 100 meters of its aiming point. Russia said it would use these missiles to attack terrorist bases in foreign countries. This it did, frequently, after Russian entered the war in Syria during 2015. The Kh-55, Kh-555 and Kh-101 were all used in Syria. A few times Russian launched these missiles from Russian air bases and used their long range to fly over Iran and Iraq to targets in Syria.
The Kh-101 had a new shape, and a radar absorbing skin, to make it more difficult for radar to detect. Otherwise, the Kh-101 appears to have the same weight, range and payload of the Kh-55. The Kh-101 wasn't meant to replace Kh-555 missiles, but complement them, at least until the Kh-555s were too old to maintain, and had to be retired. That's a process that took over a decade to happen.
At the end of the Cold War, Ukraine inherited 1,612 KH-55s. These were for use by Soviet Tu-95MS, which can carry sixteen Kh-55s or eight Kh-101s. The Ukrainian also inherited 19 jet powered Tu-160 and 25 propeller driven Tu-95MS heavy bombers. Initially Ukraine wanted Russia to pay three billion dollars to get the bombers and cruise missiles back. After years of haggling, Russia agreed to pay $285 million for eight Tu-160s, three Tu-96MSs and 575 Kh-55 missiles. The rest of the bombers and missiles were destroyed as part of an American financed post-Cold War disarmament program. In 2005 Ukrainian investigators found that a corrupt general had sold twelve Kh-55s to Iran and six to China for over $40 million. Iran later reverse engineered the missiles to build their Soumar missile. The Chinese found that the Kh-55s were similar to missiles the Chinese had already designed and put into production.
The Kh-101 is expensive (over $10 million each) because of the stealth features and guidance system which enables it to hit targets very accurately after traveling up to 5,000 kilometers. Each Kh-101 is 7.45 meters (24 feet) long, weighs 2.2 tons and carries a 400 kg (880 pound) warhead. Cruise speed is about 700 kilometers an hour although it can be programmed to speed up to nearly a thousand kilometers an hour which reduces max range to about 3,000 kilometers. Despite that, the Kh-101 proved vulnerable to Ukrainian air defenses and many were shot down. The older Kh-55s and Kh-555s were even more vulnerable but the Kh-101 was more likely to get through and hit a target. By early 2023 Russia was eliminating the missile serial number because that number also contains data on when the missile was manufactured. Without that data, often recovered from missile debris, the Ukrainians could no longer estimate how many Kh-101s were being used. Russian media revealed that Kh-101s were being used as quickly as they could be produced. While the Kh-101s are usually launched from Tu-160s carrying ten missiles or TU-95s carrying eight missiles, the Su-35 fighter-bomber can also carry two of them.