North Korea has increased its number of missile launches in the past month, including what it calls “hypersonic” weapons tests.
The country’s missile engineers and scientists may have a high profile within leader Kim Jong-un's government – but little is known about them to the rest of the world.
Analysts say Mr Kim is expected to make them part of his long-term military plans.
Here is what we know – and what we don’t – about these key personnel in North Korea.
Who are North Korea's missile scientists?
Very little is known about the mid-level and working-level scientists and technicians involved in missile research and development.
Analysts say these scientists appear to have guaranteed job security because of the resources and effort expended to educate and train them and they are sequestered to special districts so that they are neither a defection risk nor a political or social nuisance to the regime.
“Unlike economic cadres or even military commanders, this is a population that is not easily replaced,” Michael Madden, a North Korea leadership expert at the Washington-based Stimson Centre, told Reuters.
Many of them attend Kim Jong-un National Defence University, a training ground for North Korean defence-related science and technology specialists that has reportedly added a college focused on “hypersonic missile technology”.
The scientists and engineers often appear split into competing teams designing similar types of weapons, allowing them to go down numerous routes to assess which technology is the most promising, said Ken Gause, director of the International Affairs Group at CNA, a non-profit research and analysis organisation based in Arlington, Virginia.
A 2018 study by the James Martin Centre for Non-proliferation Studies (CNS) found North Korean scientists had worked with researchers in other countries to co-write at least 100 published articles that had identifiable significance for dual-use technology, weapons of mass destruction (WMD) or other military purposes.
Who leads the missile programme?
Mr Kim relies on three people to lead the secretive country’s rapidly accelerating missile programme.
They include former air force general Ri Pyong-chol, veteran rocket scientist Kim Jong-sik and Jang Chang-ha, head of a weapons development and procurement centre.
A fourth official – Pak Jong-chon, the chief of the General Staff – has also assumed a higher-profile role in the Military Industry Department (MID), which is responsible for the production of strategic weapons, according to Mr Gause.
"We have seen a lot of changes in the military industry arena in the last few years," said Mr Gause.
Mr Pak oversaw many recent tests in the absence of Mr Kim, who did not attend any missile launches in 2021 but observed one of the hypersonic missile tests in January.
Last year, Yu Jim was appointed to lead the MID. Mr Yu was previously a representative of North Korea’s primary state arms dealer in Iran, according to Mr Madden.
What are the organisations?
The Academy of National Defence Science (Nads), also known as the Second Academy of Natural Sciences (Sans), oversees North Korea's missile development.
Mr Madden said the state of a weapon's development can often be divined from who is reported to have attended a test.
An event where the only personnel are from Nads means the weapon is still at the research and development phase, for example. If an event combines Nads and the Second Economic Committee, that often means that the weapon is moving from development to production and manufacturing.
Finally, if personnel from the military’s General Staff Department (GSD) attend a test, such as the recent railway-borne missile launch, this usually indicates that the weapon is finished and will be deployed.
There are initial signals that as North Korea completes its missile and nuclear arsenal, it may fold more elements of its Strategic Forces back under GSD, signalling that it has moved to an operational role, Mr Madden said.
Does North Korea receive any foreign assistance?
North Korea’s missile programme has roots in the assistance it received from the Soviet Union, and later Russia, analysts say, and the boosters involved in propelling the latest hypersonic warheads are similar to Soviet designs.
There is debate as to what extent that assistance has continued since the 1990s.
According to the latest sanctions designations by the US, North Koreans linked to Nads in China and Russia continue to procure materials and technical information for North Korea’s WMD and missile programmes, aided by at least one Russian telecoms company and a Russian citizen.
Markus Schiller, a Europe-based missile expert, said North Korea’s success in testing suggests it has had external support.
But he noted that under Mr Kim, the country's missiles failed more often than they did in the past, suggesting that he is testing more home-grown designs than his predecessors.