CAB 13 Pattern

[Bill Alexander]

This may be obvious to the CMP enthusiasts, but please indulge me. Why was the windshield reverse sloped on the CAB 13 pattern?

[David_Hayward (RIP)]

Chevrolet # 13 CAB PRODUCTION BEGAN AT SERIAL # 284XX01524?, we believe, and then # 2844513801 OCTOBER 1942> # 13 CAB FRONT WINDSCREENS OPENED 90 DEGREES FROM ORIGINAL 30 so you can see that there were two different styles of front screen, plus the #43 Cab.

The reasons I have read are to prevent reflections off the front screen alerting aircraft, and also to reduce glare. The former may sound far-fetched but yesterday my wife and two of our kids accompanied me down the Motorway in our new Honda Jazz, which is tall for a supermini and you sit higher off the ground than usual. A Porsche Boxster was in front with a plastic screen behind the driver/passenger, which is supposed to prevent air flow throwing occupants' hair all over the place. However it is a vertical [NOTE VERTICAL ...point being it simulated a # 11/#12 screen in my mind] piece of transparent plastic. The problem was that the sun was in the west, and the vibrations of the car travelling on concrete road made it shimmy, and the sun glanced off the screen like a mirror, right into my eyes. It was like an automotive signalling mirror, only very dangerous as it nearly blinded me and others. This proves that the reflection off a CMP #11 or # 12 cab screen in sunny conditions could easily have been a beacon to enemy aircraft, and also been dangerous for drivers in front of or passing in the opposite direction.

[Hanno Spoelstra]

Bill,

It isn't so obvious as many people think! As David said, one often reads the windshield on the Cab 13 was reverse sloped to prevent reflections off the front screen alerting aircraft. But then why would the windshield be allowed to open upward? The glass then still reflects sunlight upward!

The second reason David listed - "to reduce glare" - was the real reason, I believe. This is endorsed by a quote from page 208 of the Third Edition of the Ford Instruction Book Special Pattern Vehicles:
"The windshield slants forward placing the surface of the glass square with the driver's line of vision to the road and reduces the possibility of reflected light interfering with the driver's vision. It is exceptionally effective during blackout operations."

Regards,
Hanno

[David_Hayward (RIP)]

Yes, this must be the only genuine reason...allowing the screen to open up to 90 degrees defeats the whole object if it was an anti-aircraft idea. It simply does not wash. However with the screen sloped it would reduce glare, and then shifting the glass out of the eyeline after 30 degrees was demed insufficient also makes sense. Of course with the #43 cab you still had the sloping screen but in practice in sunny climes would the screen have been removed completely, and goggles worn?

[Don Dingwall]

Was headroom.

Those of us who have #11 or 12 cabs know this well. It was an easy way of increasing headroom while not moving the bottom line of the windshield froward, thus restricting access to the engine even more.

Don

[Brian Gough]

and GM said in

Service Information Bulletin B-18, dated October 20, 1942, item 30, Windshield Opening Revision.

“The windshield throwout arms “A” Fig. 1 have been revised on the new style cab to increase the windshield opening by changing the arc through which the windshield travels from 30 degrees to 90 degrees, Fig. 1. This facilitates the use of Fire Arms through the windshield opening and became effective commencing Serial 2844409695 on all Canadian Military Pattern Vehicles, except Heavy Utility when the change was made commencing Serial 2844513801.”


Brian

[Keith Webb]

Originally posted by Brian Gough
and GM said in

Service Information Bulletin B-18, dated October 20, 1942, item 30, Windshield Opening Revision.

?The windshield throwout arms ?A? Fig. 1 have been revised on the new style cab to increase the windshield opening by changing the arc through which the windshield travels from 30 degrees to 90 degrees, Fig. 1. This facilitates the use of Fire Arms through the windshield opening and became effective commencing Serial 2844409695 on all Canadian Military Pattern Vehicles, except Heavy Utility when the change was made commencing Serial 2844513801.?


Brian

Aussie built cab 13s all had 90 degree opening windscreens - on some Fords you will see footman loops along the brow above the windscreen - these were for attaching canvas bags to cover them when fully open.

Keith

[cletrac (RIP)]

On the Western desert images thread there are several pics of trucks with painted windshields or canvas covers on them. This is obviously to avoid aircraft detection.
http://www.class-five.com/~mlu/forum...7&d=1266072014
http://www.class-five.com/~mlu/forum...9&d=1266072103
http://www.class-five.com/~mlu/forum...8&d=1266176392
http://www.class-five.com/~mlu/forum...4&d=1266071743
http://www.class-five.com/~mlu/forum...9&d=1266201127
The last one even has the camo pattern on the windshield. None of these other reasons would apply here and North Africa is where the Brits learned the lessons needed to apply to a new truck design. For instance the roof hatch for aerial observation.
http://www.class-five.com/~mlu/forum...5&d=1266146444

[oztankboy]

Originally Posted by Keith Webb

Aussie built cab 13s all had 90 degree opening windscreens - on some Fords you will see footman loops along the brow above the windscreen - these were for attaching canvas bags to cover them when fully open.

Keith

Also with Aust Chev's along the top edge of the windscreen there are "clitch" fastners for the canvas covers. I infact have a sample of the Ford type.

Another reason I have read for the reverse slope windscreen was to prevent the the build up of snow on the the windscreen... something we rearly have to worry about here in Australia. An interesting note is the the Aust Army 4x4 and 6x6 Inters mfg in the late 50's to the early 70's had this feature.

Talking from experience it also did help with blackout driveing but the best of all was to open the winscreen.

Phil...