Japan's Railgun Takes The Sting Out Of China's Hypersonics

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A ship-based railgun could fire multiple programmable rounds that simultaneously release a payload of hundreds of metal balls in a shotgun-like fashion, which could shred swarming smaller craft or suppress large-area land targets. Should precision be required, a solid projectile could be used, maximizing damage against a point target and minimizing collateral damage.

Railguns may be a cost-effective means to deal with saturation missile attacks, compared to interceptor missiles, which are priced in the millions per round. Japan's railgun push comes as China fields DF-17 hypersonic glide vehicles (HGV) and CJ-10/100 cruise missiles capable of evading current defenses, and North Korea advances its ballistic missile program .

In terms of missile defense, railguns may be assigned terminal interception tasks. Currently, Japan employs a two-tier missile defense system consisting of Aegis-equipped destroyers for mid-course interception and Patriot for terminal interception. However, this is not a complete missile defense system.

A ballistic missile has three distinct phases of flight: boost, midcourse and terminal. The boost phase begins immediately after launch and ends when the missile leaves the Earth's atmosphere, after its rocket motors have burned out.

While this would be the ideal phase for interception, it has a very short window of three to five minutes for intercontinental ballistic missiles (ICBMs) and even shorter-one to two minutes-for smaller missiles. A boost-phase intercept also requires interceptors to be close to launch sites, which is not ideal for Japan, given its relatively distant location from China and North Korea.

During the midcourse phase, the unpowered missile travels in a predictable ballistic arc before re-entering the Earth's atmosphere. While this phase offers the longest time window for interception using systems such as Aegis, it also allows the missile to deploy penetration aids, including decoys, electronic warfare and multiple independently targetable reentry vehicles (MIRVs), which increase the difficulty of a successful interception. Mid-course interceptor missiles, such as the SM-3, are also scarce and costly at US$27.9 million each .

At the terminal stage, the missile or its warheads re-enter the atmosphere at hypersonic speeds, giving an interception time of less than one minute. At this stage, military bases, population centers and critical infrastructure serve as potential missile targets for point defense systems like the Patriot.

However, as with the mid-course SM-3 interceptor, Patriot interceptors are in short supply and pricey at $4 million per missile . Also, as seen in Russia's use of the Oreshnik intermediate-range ballistic missile (IRBM) with conventional MIRVs against Ukraine, terminal defense systems such as Patriot may be ineffective against such threats.

A ship-mounted railgun may address these vulnerabilities of Japan's missile shield, reinforcing its mid-course and terminal phase interception capabilities. Its mobility could enable it to fill in coverage gaps between Japan's Aegis and Patriot systems.

A fast-firing, gun-based defense system could compensate for the weaknesses of missile defenses by firing numerous rounds quickly, similar to the US counter-rocket, artillery, and mortar (C-RAM) systems, but on a larger scale.