Vehicular Land Navigation System C1

[David Dunlop]

You continue to amaze, Ed! Thanks for posting that!

Who built them and when, and how long was the system in service?


David

[Lang]

The direction indication would only have been reasonably accurate for an hour or so before resetting due to gyroscopic precession (caused by drag on the gyro bearings among other things) but this would normally be enough for most purposes. In a steel vehicle it would be almost impossible to fit a remote magnetic compass (as in aircraft) to feed continuous updates to the gyro to correct the drift.

Where they got their correction from I can only guess - the most obvious is for someone to stand well back from the metal mass of the vehicle with a prismatic compass and call out the centreline direction to be wound on to the indicator. If you were really stuck inside for long periods an educated guess could be taken from experience with that particular instrument to wind on 10 degrees, or whatever, East or West every hour.

The beauty of a gyro system is you can put anything you want on the dial so you can have true bearings to read straight off the map without worrying about magnetic variation calculations.

I think they were probably meant for circumstances such as an assault on a pitch black night or if you needed to be closed up (Churchill?) for comparatively short periods.

Lang

[Grant Bowker]

The EME instruction to install the "NAVIGATIONAL SET, Land Vehicular, C1" in the M38 is dated July 1963. My copy came with several other EME instructions M38 and M38A1. There wasn't a similar instruction for the M38A1 in the bundle. I don't know whether that was because it was never done (obsolete???) or if the same instructions were used (seems unlikely as there were other mods where separate sheets existed).
The NSN for the Nav set was 6605-21-111-1843.

[Ed Storey]

The Navigational Set, Land Vehicular, C-l, (NAVAID) was developed to provide a self-contained navigational aid, independent of radio assistance, which would give positional and navigational information to commanders of vehicles in armoured and other units under the following conditions:
(1) Closed-down, during mobile operations by day or night, and under nuclear threat conditions.
(2) During conditions of darkness and poor visibility, e.g., fog and smoke.
(3) On featureless or poorly mapped terrain, including the Arctic.

Despite the ease of operation and advantages that were provided by the NAV AID, the art of map reading was still of primary importance and was not to be neglected.

The equipment did not require radio assistance for its operation and by using a gyro-compass it is was affected by variations in the earth's magnetic field or in the magnetic characteristics of the vehicle.

This device was designed to indicate the location of vehicles to within an average accuracy of 1 % of the distance travelled and the heading to within .75 degrees.

This device could be used in unmapped terrain. Under these conditions the· counters on the Indicator Heading and Position were set to an arbitrary reading and an X (representing the present position of the vehicle) marked on the plastic map holder of the Plotter with a china pencil. The vehicle could return to the original start point, after completing a mission, by the commander directing the arrow of light, which corresponds to the movement of the vehicle) toward the X until the arrow returns to the X. The counters were then checked to see that they reflect the arbitrary reading set at the beginning of the mission.

The NAVAID could only be used maps with scales of 1/25,000; 1/50,000; 1/100,000 and 1/250,000. Prior to the first run of the day, the Compass required an initial 30 to 60 minutes warm-up and settling period. The compass had some difficulty maintaining its design accuracy at the higher speeds encountered in road travel. When moving over hilly terrain, the actual distance travelled on the ground is greater than the distance travelled
on the map. Therefore, periodically, the actual heading and position on the ground had to be checked against the heading and position displayed by the NAVAID. If there was a variation appropriate adjustments had to be made.

[Lang]

Ed

As you point out the difference between design accuracy and real life can be quite large. Claiming an accuracy within .75 degrees is a nonsense (about half the width of the needle) - a train driver would be lucky to achieve that!

I defy a 747 captain to hand fly his aircraft just using flight instruments (no GPS or radio aids) over any distance without drifting 2 and probably 5 degrees each side of heading. Driving a vehicle, particularly a skid steered tracked vehicle, over uneven terrain would produce a champagne celebration if they kept inside 10 degrees.

Still it is better than having the enemy watching out of mild curiosity as an entire tank regiment scattered to the four winds during a closed up advance.

Lang

[David Dunlop]

Grant, it is interesting your manuals for the M38 take this system back to it's possible roots in WW2 with the MB/GPW system.

A couple of years ago, while looking for C42 Set information on line, I stumbled into the National Archives site in London, England. They had two sequentially listed documents in their files for a "Vehicle Land Navigation System XC1". One was an initial report, the other the final report, both dated simply 1961, with a very cryptic Canadian reference. These were not online documents but had to be viewed in person or ordered blind. Struck my curiosity but not enough to follow up on, and with the "X" prefix for 'Experimental', my other thought at the time was it probably never saw the light of day.

Now it appears the system did indeed see some level of production volume, with intent for installation in a variety of vehicles. Very intriguing and whets the appetite for more information about it.

David

[Ed Storey]

There are NAVAID Installation Instructions for both the M38A1CDN and M37CDN as well as the M38CDN mentioned earlier.