Monday, October 14, 2013

Navigating the USS Midway

When launched in 1945 just days after the end of WWII, she was the largest ship in the world, and is still mightily impressive today. There are many who tell her history, and of the 225,00 sailors who lived on her during 47 years of service. I will leave some links behind for you to explore. I had some spare time during the NMEA conference, and visited the USS Midway Museum, a most worthy way to spend a few hours. Today we are talking about some of her navigation gear history. The USS Midway offers a slice of navigational equipment history spanning two generations.

This is a view of the Midway's island now frozen in 1992 time. It bristles with antennas, radar arrays, and pods. Like the Midway when she was shiny new, it represents the best money could buy in navigation systems at the time. The 1992 Midway sported GPS satellite technology, inertial guidance system, and something the original Midway never had... computers.

As you can see the 1945 Midway's island also bristled with similar gear, albeit of a more vintage form. At the time she was state of the art. There was radar, LORAN, radio direction finder, and sonar. Let's not forget the venerable sextant, and all of that height of eye stuff either. In many places in the 1940's world a sextant was still very much needed, and one is still on the ship today along with the paper charts.

With the advent of computers, came the development of inertial guidance systems, or from the Navy's acronym driven viewpoint the "SINS" (Ships Inertial Navigation System).

The rounded device in the center of the photo that's about the half the size of a Volkswagen is a Sperry gyroscope. As you can see, it is substantially attached physically to the ship. Inertial navigation systems need three elements to work. A gyroscope, accelerometer, and a computer.

The gyroscope is a wheel spinning in gimbals. When the ship moves, the gyroscope reacts to this and the direction of travel can be determined. If you add an accelerometer you can measure the velocity. From these two factors you can calculate direction, speed and distance you traveled, to a point. All gyroscopes have some drift. This is caused in part by mechanical friction, and the inability to measure the gyro's angular deflection with extreme precision. The accelerometer also suffers from a similar problem. This drift over time causes position, and distance traveled errors to compound. At some point, you have to update it with an external position fix source such as a sextant, LORAN, GPS or other methods.

The navy first adopted SINS in 1960 in submarines in part to provide ships navigation, and to also initialize the position for the nuclear missiles they carried. This allowed only occasional contact with the surface to re-calibrate the gyro's position. From the Navy's perspective the SINS offered another big advantage. Unlike radio frequency based navigation systems, the SINS systems could not be jammed.

This is the time computers start to become small enough to actually be installed on a ship. The Midway's SINS system is circa 1963 and its computer is a Univac CP-642B. This was the miracle of computers at the time. No tubes, 9500 transistors, and 979,860 magnetic cores providing a whopping storage capacity of 32K. It came with the modern media of punched paper machines, and reel to reel tape drives.

Best of all this amazing piece of early computer hardware was designed to have a mean time between failure of over two hundred hours. That meant it was expected to run for at least eight days in a row before something broke. This gave new meaning to being on the bleeding edge of technology, and the need for a lot of spare parts.

Just to provide some perspective on how far we have come in the intervening 50 years, the entire USS Midways SINS system can now be replaced with a $80.00 credit card sized digital inertial motion unit, a lap top computer, and a GPS.
The next big jump in the Midway's nav tech was the introduction of GPS. Scientists listening to the Sputnik developed the concept that if the orbit was known, the transmission's Doppler shift variations could tell you where you were.

This starts with the Transit system which became fully operational around 1964. The first successful launch of a Transit satellite was in 1960, barely three years after the Russians launched Sputnik.  In the beginning it might take an hour to get a fix that was plus or minus 120 meters. By 1980 it would take less much less time to get a fix and the accuracy improved to about 3 meters.

This brings us to the interesting gray box above. This is a Magnavox radio navigation receiver, also commercially known as the Magnavox Satellite Omega Navigator circa mid eighties I think.

These units were the Swiss army knives of modern navigation systems, and bridged the rapidly evolving technologies. Depending on the vintage starting in 1976 they received Omega (the first global LORAN style system), LORAN, Transit, and Navstar signals which have morphed over time into our modern day GPS. This covered almost all of the radio navigation technologies starting with USS Midway's commissioning in 1945 to 1992. 

There were many things I hoped to see, but didn't. That doesn't mean they weren't there, but the ship is huge, and only a portion of it is yet open to the public. I'm hard pressed to believe the ship was still using the Univac computer in 1992. I do believe however it would have been cheaper to leave it there than remove it. It weighs over a ton and is water cooled. I suspect that the Magnavox genre of equipment would have long been used as the position update source for the SINS system. When decommissioned a lot of more modern equipment was removed for security reasons, or rendered inoperable.

It was an eye opening experience to visit the Midway. Among the docents are people who served on the Midway, and flew the aircraft. The exhibits are profuse, and expect to spend at least half a day to see most of the vessel. The short wait to tour the Island is worth every second. Some of the ladders (steep stairs) can wind you, and watch your shins at all times. Those bulkhead door sills can bite hard. The one last piece of tech I liked were the phones. There are purportedly 1500 of them on board. It's not that the handsets are notable, it's one of the brass cradles I would like. Good thing I left my screw driver at home.

Here is a brief marine navigation technology timeline:

Compass - 206 BC to present
Mariners Astrolab - 1265AD to 1757
Nautical Charts - 13th century to present 
Modern Sextant = 1757 to present
Mariners Radio Direction Finder - 1902 to present (very limited use now)
LORAN - WWII to 2010
Inertial Guidance system - WWII to present
Transit GPS - 1960 - 1996
Omega Radio Navigation - 1971 to 1997
Navstar - 1974 to present
GLONASS GPS  - 1976 to present

USS Midway Links:

Wikipedia on the USS Midway.

The Midway Museum. (Many more links from here)


  1. Great article. One of the consistently interesting features of visiting old warships-- especially the larger ones with hulls that were hard to replace-- is seeing the layered technology plastered onto these vessels over the years. Last year I had an opportunity to tour such a vessel at Sydney Australia's excellent maritime. Looking at the combat information center, communications rooms and other hubs of information activity on the ship, it struck that one good reason this vessel may have been retired was simply the increasing confusion of displays and controls for crew to deal with. Fully removing this stuff isn't easy, especially the wiring. The passageway overheads on the ship in question were simply jammed with cables, leaving little room for addition and probably posing an impossible challenge to quickly repair if damaged.

  2. Nice stuff, Bill. We toured the roughly contemporary HMCS Haida over the summer: probably about the size of USS Midway's tender, but she saw some real war. I wrote about it here: