NavList:

Frank, you asked us, "How far was Nautilus from the pole (guesses welcome) at that moment when the sub's captain and navigator signed off on that little nav receipt that says latitude 90°00.0'? Five miles? Fifty miles?? More?! "

I have a guess, maybe 100 miles. And that's a guess backed up with some detail from the polar voyage in that book "Submerged". There is another account of the 1987 trip at https://www.globalsecurity.org/military/library/report/2001/arctic.htm

internet history: you can almost smell the early years of this century in that URL... it ends in ".htm" Haven't seen one of those in a while :-o

The submarine was a special ops (spy) boat called "L Mendel Rivers" one of the rare ones named for a member of Congress. Follow the money!! Of the SINS on that submarine, the author at globalsecurity. org says,

L. Mendel Rivers was the last submarine on the East Coast still to be equipped with the venerable Dual Miniature Inertial Navigation System (DMINS). For years, this equipment has guided submarines safely in submerged transits, and has proven much more capable than the older navigation systems onboard USS Nautilus (SSN-571) or USS Skate (SSN-578) when they first transited below the Arctic ice. As this story will relate, however, there are serious hurdles to overcome when navigating a submarine in extreme northern latitudes. Gyros, which provide heading, and gyro-based inertial navigators, which provide position, do not function normally at the North Pole because the tangential components of the earth's rotational velocity are minimal. Even knowing this in advance, and looking forward to the unique challenges that lay ahead of us, we got more than we expected.

So like Frank said, this DMINS system was more advanced than the earlier Inertial Navigation System on USS Nautilus, but still primitive. And there's a story that seems to explain better that electrcal fault described in "Submerged". This author says,

Despite our preparations and training, isolated equipment problems on our 26-year-old boat kept us busy. The first bump in the road was the failure of our electro-magnetic (EM) log's lower pit sword, which provides speed input to the ship's navigation systems. This required us to drive the 15,000-mile journey using what is known as a "dummy log" to input ship's speed manually. Operating DMINS in the undamped mode, which was necessitated by the loss of the normal EM log input, required frequent attention from the watchstanders. Surfacing through the ice every three to five days for fixes and system resets became common.

Next we get some real celestial navigation. They have no bearing both because of the longitude problem right there at the north pole, and that's true even if they only "thought" they were at the pole, and also because of their electrics fault

The Captain calculated our heading by shooting a relative bearing to the moon and computed its Greenwich Hour Angle from the Nautical Almanac. This told us what longitude line the ship was pointing. We verified this by using a hand held GPS receiver topside, marking bow and stern waypoints and checking the bearing between them. With this information, we submerged the ship, executed a turn, recalculated our final course, and said a prayer as we headed south away from the pole to find another suitable place to surface the ship and restart our gyroscopes.

Nice, right? And then how to steer a straight course from the pole? They used a very old trick with a modern twist. With a large enough vessel, you can see you wake astern for many miles. It's like a road across the sea, and in tropical waters that road sometimes glows green at night! Keep your wake straight, and your course is straight, too. On a submarine, you do that with sonar! Keep the sonar signature of the wake minimized, and that means your wake is dead astern.

Now the bad navigation solution emerges...

We drove 180 miles away from the pole at flank speed in deep water. We were able to approximate driving a straight line by keeping the stern marker line on the sonar display centered on own ship's sound trace in relative display mode - in other words, we "looked" backwards to make sure our wake was straight. As the Assistant Navigator, I knew that our chances for a pinpoint, hand-calculated dead-reckoning (DR) position were slim after 180 miles. When you combine unknown currents and helm error, and compound this over time, your error grows continually.

After the 180-mile sprint was complete, we found a surfaceable feature and punched through. The moment of truth had come. The GPS fix indicated that we were on the exact latitude line the quartermasters had calculated by the hand DR, but the heading error placed us 145 nautical miles due east of that position! That was tough to swallow.

They did everything right. The trick with the Moon's GHA is foolproof. Bearing from wake by sonar is also foolproof (speaking from personal experience). So how did they end up 145 nautical miles wrong after a run of 180 miles? Maybe twenty miles from currents, DR uncertainties, and errors in heading (even with the wake trick). But that leaves something like 120 nautical miles. That's a BIG error for a nuclear boat. The simplest explanation is that their starting position was wrong! They were not at the pole. They may have been over 100 nautical miles from the pole when they started their run. Their inertial navigation system got them rather close to the pole, but like those navigators on sleds in the heroic era of polar exploration, you could only get close.

Josh Carty