Russia is equipping its new nuclear-powered submarines with hypersonic Zircon missiles, the head of Russia’s largest shipbuilder said in an interview published by the state news agency RIA Novosti on Monday, Reuters reported.

“Multipurpose nuclear submarines of the Yasen-M project will … on a regular basis be equipped with the Zircon missile complex,” General Director of the United Shipbuilding Corporation (USC) Oleksiy Rakhmanov told RIA Novosti.

“Work in this direction is already underway.”

Yasen-class submarines, also known as Project 885M, are nuclear powered cruise missile submarines built to replace Soviet-era nuclear attack submarines as part of the Army and Navy modernization program.

Zircon hypersonic missiles have a range of 900 km and can fly at several times the speed of sound, making it difficult to defend against them.

Earlier this year, President Vladimir Putin said Russia would begin mass deliveries of Zircon missiles, which he said are “invincible,” as part of the country’s efforts to strengthen its nuclear forces.

The Russian frigate Admiral Gorshkov, which tested its strike capabilities in the western Atlantic earlier this year, is already equipped with Zircon missiles.