The B-21 Raider is here and you might be wondering why do we even need it. The US has 100s of ships and submarines that can launch cruise missiles easily from anywhere in the world. There are land based and sea based ballistic missiles serving as the nuclear deterrent. The thing is, these ships are good options for less than peer conflicts, peers can hunt them down using long range missiles and satellites. The US still needs its massive bomber fleet and I split the overall reason why B-21 is needed into three factors, hope this helps.
Factor 1: Credible anti-ship capability
Conflicts in the middle east utlized naval assets launching cruise missiles from a 1000 km away in international waters, also well outside strike circles of any enemy assets. The thing is, DF-21 has a 1,700 km on paper attack range which means any TLAMs launched outside the bubble cannot use low-low flight profiles to stay under the radar on the way to the target and their subsonic speeds makes interceptions relatively easy. Only the JASSM-XR might be able to penetrate peer defenses due to its VLO design at that ranges (please add any missiles I missed in the comments below).
CGI vs Actual, pre-unveil Raider!
Thus the presence of any long range anti-ship missile creates a bubble where credible satellite based detection can doom a ship. Modern missile warheads with potentially steerable re-entry vehicles can make hitting moving targets very easy. Also, at the end of the day the presence of such a system is a bigger deterrent than its accuracy on paper because no one is going to pubhlish full up test information. Given that China has built rail mounted concrete carrier mockups for ballistic missile tests also shows that they are serious about the system and are aggressively working on it.
Post Unveil Raider looking Smart
Factor 2: Speed of Response
It is very simple, a ship takes days to get into launching position, it is difficult to ensure that it cannot be seen and it is even more difficult to do so in the current satellite rich environment where multiple passes happen every single day. A jet-bomber deploying from an airbase can cover thousands of kilometers in mere hours and with the size of this thing and the US supremacy in making sure its tanking capabilities are well oiled ops beasts, even from continental US, a bomber can strike anywhere within a day
A CGI of what the Raider will look like in the air!
For eg., the B-2 has flown multiple 30 hour non-stop missions from their bases to Kosovo, to Afghanistan, to Libya, to Iraq and to South Korea (in separate missions, obviously) meaning the USAF has worked out such long duration missions and regularly practises it. It shows that the B-21 can basically strike anywhere by the time a naval asset is put to sea or gets anywhere close to the launch area for missiles.
Factor 3: Flexibility of Launch
A ship, as stated before takes days to get into position. Whats worse is that they are slow and they limit the options of where to launch from, given the importance of time. A bomber can easily change course and get on a heading that provides the best launch to target destruction probability and the highest chance of survival for the crew. The biggest advantage of any air asset is flexibility. Given modern layered air defenses, you have to ensure that your launch point is away from airborne or ground based tracking and missiles can use low level flight profiles and use terrain to mask their approach.
Kinda loved the B-2’s design, when they were the cutting edge.
You might have noticed that I didnt even mention the traditional fly over a target and drop a bomb role. Modern conflicts have LR-SAMs to MANPADS in active war zones which will see incoming aircraft at much closer ranges. Once enemy AD is suppressed, maybe then the strategic bombers can do this. Until then, the role of close air support falls on tactical jets and strategic targets are hit by cruise missiles. I also didnt mention this role because stealth and by extension B-21 is designed to be used in the first days of war against an enemy that is fighting fit and not one that has been bombed down.
Given these factors, it is important for the US to have an edge in the world that is becoming increasily multi-polar. All countries are headed in their own directions where they are seeing very little if any overlap in political directions being taken. These make an environment where saber rattling becomes more and more common. The Chinese and the Russians are using their Tu-95s and H-6s for joint patrols as their show of force. It only makes sense for the US to stay at the edge of bomber tech and push it further.
Picture Credits: USAF and Northrop Grumman