How to navigate a sub without GPS

141125-N-DB801-137 PEARL HARBOR (Nov. 25, 2014) The Virginia-class attack submarine USS Mississippi (SSN 782) arrives at Joint Base Pearl Harbor-Hickam for a change of homeport from Commander, Submarine Squadron (SUBRON) 4 in Groton, Conn., to SUBRON-1. Mississippi is the 4th Virginia-class submarine to be home ported in Pearl Harbor, and one of 18 attack submarines permanently homeported at the historic base. (U.S. Navy photo by Mass Communication Specialist 1st Class Steven Khor/Released)

Concerned that its submarines are becoming too dependent on GPS, the Navy wants a system that will enable subs to navigate when GPS is jammed or otherwise unavailable.

The Navy wants a solution that will “make use of existing sensors – imagers, antenna, gyroscopes, etc., with only limited allowance for new associated inboard hardware support equipment (6 to 8 inches in a 19 inch diameter rack that could be located inside the submarine hull which allows for more flexibility),” according to the Navy research proposal.

Resource: Read the Proposal

The Navy suggests that navigational sources might be magnetic, astronomical, or light-based. But the proposal makes clear that anything involve active transmissions — which presumably might give away a sub’s location — is not acceptable.