Important update on this article: April Fool’s

American submarines will further extend their advantage in the undersea domain. In the first of a kind, the U.S. Navy has fitted a new form of propulsion, magnetohydrodynamic drive (MHD), to a Virginia class submarine. This promises to make the submarine virtually undetectable, the holy grail of naval warfare.

The Magnetohydrodynamic drive is being developed under the PUMP program by DARPA (Defense Advanced Research Projects Agency), first reported in 2023. Water passing through it is accelerated by means of a magnetic field using superconducting magnets. This is often likened to the way a caterpillar crawls leading to the colloquial term ‘caterpillar drive’.

The first boat to be fitted with the new propulsion will be the USS Montana (SSN 794). This Virginia Class attack submarine was commissioned into the U.S. Navy in June 2022. Although still a new boat, she has been brought in to Groton, Connecticut, for the modifications.

Quietest Submarine Propulsion Ever

It is likely to be particularly stealthy as there are no moving mechanical parts. This will make the submarine particularly difficult to detect using passive sonar which listens for noises emitted by the targeted submarine. Sonar operators searching for the USS Montana will likely hear noises which are indistinguishable from natural phenomenon, such as seismic activity.

Instead of a traditional propeller at the stern, the new propulsion will be entirely within the submarine’s hull. According to British experts the only external clues are likely to be the water intake doors in the bow. These will resemble torpedo tube shutters but larger, approximately the diameter of a submarine launched ballistic missile. But mounted horizontally, which is unusual for those missiles.

It Is Time

The new propulsion may be fitted to more submarines if the trials are successful. These are likely to include new-build Virginia class attack submarines and the future ‘SSN-X’ type. It is unlikely to be fitted to the Columbia Class ballistic missile submarines (SSBN) however as this would likely constitute a first strike capability. There is no reason to make a nuclear deterrent submarine so stealthy if it is only intended for retaliatory strikes.

USS Montana is expected to undergo sea trials on the Penobscot River in Maine. This will make it more difficult for the Russian Navy to observe the tests.

The caterpillar drive propulsions is still in its infancy. Whether the Penobscot River will be the end of the story, or the beginning of a new chapter, remains to be seen. Either way, Montana will remain unseen.