“Bob Tail” radiometric device

(USSR)

Notes: This navigational sensor, properly a radiometric sextant, was carried by some of the Kiev class ships and the first two Kirov class units. It was based on the “Cod Eye” device carried by Soviet SSBNs and the earlier Kiev units.

The “Bob Tail” obtained a very accurate fix by bouncing a powerful electromagnetic pulse off a known space object, such as the moon. In the era before GPS and GLONASS, existing SATNAV systems did not cover all latitudes and shore-based aids like LORAN could be jammed or destroyed during wartime.

The topside component was two spherical antennas, containing an angled dish topped with a non-magnetic foil dome.

This type of navigational fix was normally used for precise launches of ballistic missiles. In the case of the Soviet surface ships, it appears it was to be used for a accurate fix to launch nuclear-variant “Shipwreck” or “Sandbox” missiles against area shore targets such as ports or airfields. A “Bob Tail” fix was much more accurate than dead reckoning, and slightly more accurate than a visual fix using a traditional sailor’s sextant and constellations. The advantage of this system was that it could be used anywhere on Earth, and in daytime or under overcast skies. The disadvantage was that valuable space and weight were allocated to large antennas and processors that realistically saw little use.