Prompt Global Strike (PGS) involves creation of offensive weapon systems that are able to deliver a blow with non-nuclear weapons at any point of the planet within an hour after the decision.
Under the Conventional Trident Modification program, each of the dozen deployed U.S. ballistic missile submarines would have two of their 24 Trident nuclear-armed ballistic missiles converted to carry conventional payloads.
The most feasible implementation of the concept would be using Intercontinental Ballistic Missiles (ICBM) armed with high-precision conventional warheads, while a second component may be strategic cruise missiles. A third component envisages the creation of advanced delivery vehicles capable of exiting and re-entering the atmosphere, though such developments face the problem of carrying heavy warheads and avoiding the militarization of space
This was based on an assumption that shorter-range conventional weapons might not happen to be deployed where they are needed most when an urgent target arises
The idea behind developing conventional prompt global strike weapons has been to create viable alternatives to using nuclear-tipped long-range missiles during crises in which an important target surfaces but no U.S. or allied conventional forces are available in the area. Examples of such an urgent target might be a terrorist leader spotted at a remote safe house or a North Korean atomic weapon being prepared for imminent launch.
Chinese analysts view PGS as part of a larger U.S. effort to achieve “absolute security,” with Ballistic Missile Defense (BMD) as the shield and PGS as the sword, such that Washington is able to act preemptively. Given its lower threshold of taboo on use, Chinese analysts tend to view U.S. PGS as a threat to Beijing’s conventional and nuclear weapons systems, as well as its command and control centers. With the breadth of U.S. platforms defined as PGS-related systems in China, its analysts have not ruled out their delivery of nuclear weapons. Despite its criticism of the United States, China’s BMD tests in 2008 and 2010, as well as its own test moving towards PGS in 2014, show that it is seeking similar systems.
Russia is working on countermeasures:
The Russian strategic community has repeatedly expressed concern that U.S. high‐precision conventional weapons could be used to hold Russian nuclear forces at risk.
“A number of scientific research works as well as experimental and design works is under way in the context of possible threats related to launching works on global attack with the use of hypersonic technologies on the part of the United States,” said Borisov.
“The supply of the “Yars” and “Bulava” missiles is in high gear, the works on a heavy missile are in full swing,” Borisov noted. According to the Deputy Minister, the creation of a new heavy intercontinental ballistic missile is also in strict accordance with the schedule