Instead of gunpowder, railgun technology uses electromagnetic energy to fire a projectile along a set of rails at ultra-high velocity.

The round will then in theory destroy the target, which could be an enemy ship, drone or incoming ballistic missile, solely with its vast kinetic energy.

Other countries, including the United States, China, France and Germany, are also developing the technology, but Japan's navy last year claimed a world first by test-firing a railgun on a ship.

"A railgun is a gun of the future that fires bullets with electrical energy, unlike conventional artillery," an official from the Acquisition, Technology and Logistics Agency (ATLA) within Japan's Ministry of Defence told AFP.

"It is expected that threats that can only be dealt with by railguns will emerge in the future," said the official, who did not want to be named.

The three-day DSEI Japan Conference defence fair, which began on Wednesday, comes as Japan adopts a more assertive defence policy and looks to sell more military equipment to other countries.

In particular, Japan's Mitsubishi Heavy Industries (MHI) and Germany's Thyssen Krupp Marine Systems (TKMS) are competing for a major contract to supply the Australian navy with new warships.

Winning the multi-billion-dollar Project Sea 3000 contract to supply Australia with Mogami-class frigates would be Japan's largest postwar military export order, according to Japanese media.

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MITSUBISHI HEAVY INDUSTRIES