The pace of North Korea's weapons program seems to be increasing, raising speculation that it may be trying to upgrade its arms before the deployment of a controversial US missile defense system in South Korea.
The simplest way to bypass a missile defense system is to just launch more missiles than it can effectively intercept, says Jeffrey Lewis, director of the US-based East Asia Nonproliferation Program
"Launching them simultaneously is more difficult for a missile defense system," he says. .
If those missiles are equipped with nuclear warheads "they don't have to get too many up in the air and past the missile defense system to have an effect."
Multiple missiles fired
On Monday, three ballistic missiles fired from a base in the west of North Korea flew across the country
and fell into the East Sea, also known as the Sea of Japan.
All three landed within 250 kilometers of Japan's Okushiri Island, the country's Defense Ministry said in a statement.
The accuracy of the multiple missile launches suggested North Korea's technology was improving, Japan's Defense Minister Tomomi Inada said.
Tensions have raised considerably on the peninsula since Pyongyang allegedly successfully tested a hydrogen bomb
in January. Friday's nuclear warhead test heightens tensions even further.
North Korea's weapons tests also come amid negotiations between South Korea and the US to deploy the Terminal High Altitude Area Defense system
South Korean Defense Minister Han Min-koo said last month that THAAD
is expected to be fully deployed by the end of 2017.
Lewis pointed to another way North Korea can potentially bypass THAAD's defenses: via a submarine-launched ballistic missile.
Pyongyang appears to have successfully tested such a missile last month
, much to the jubilation of Kim, as seen in photos released by North Korean state media.
"THAAD has a forward-looking radar with a 120-degree field of view," Lewis wrote in a recent report for Arms Control Wonk
. That means "North Korea's submarines would not have to travel very far out to sea to attack the THAAD system from behind."
The missile could also be mounted on a truck and deployed on land, in the manner of the Chinese DF-21, which forms a major part of that country's nuclear arsenal, Lewis says.
Firing a missile nearly straight up, whether from submarine or land, would also increase its effectiveness against THAAD. According to a report
(pdf) by the US Defense Technical Information Center, THAAD tests show it achieved its lowest possible rating against intermediate-range missiles of the type Pyongyang appears to have been developing.
"THAAD might be able to handle the KN-11, but it is distressing that North Korea can already present a threat that stresses defenses not yet deployed," Lewis writes.
Recent tests show "may be a signal that Kim Jong Un is seeking to diversify his deterrents in a way to create some strategic ambiguity," says Alex Neill, a senior fellow at the International Institute for Strategic Studies Asia
While any missile that passes Seoul's defenses would be potentially devastating for those in its path, the true threat posed by North Korea to its neighbors comes from its purported ability to equip such weapons with nuclear warheads.
Pyongyang claimed in March that it has successfully miniaturized nuclear warheads
, a crucial step to their mounting on an intermediate or long range missile. US officials said it was "prudent
" to take North Korea's word regarding this development.
"The North's nuclear capability has quite consistently been underestimated," says Neill, adding that it is safe to assume Pyongyang would want to add nuclear-capabilities to any new parts of its arsenal.