How do you differentiate between a 30 cwt and 3- ton

[Shane Lovell]

Colleagues

My question is how do you externally distinguish between a CMP 30 cwt and 3-ton truck. My question relates to the following quotes taken from Royal Artillery Notes No 1 dated 5 January 1943


Anti-tank traction

The recent more rapid development in anti-tank weapons has led to corresponding problems in the development of suitable methods of traction for the various equipments. At present, the development of the gun has got ahead of that of the vehicle, but urgent steps are now being taken to produce the necessary vehicles.

The situation is best summarised by taking each vehicle in turn, and showing what it is doing now, and what it is intended to do in the future.

(i)30-cwt 4 x 4 anti-tank portee

Designed to carry the 2-pr. Gun, but at present being used by some units to tow the 6-pr. This vehicle is now obsolescent in R.A. units, since it is being replaced by the 3-ton portee, as production permits.

(ii) Not included

(iii)3-ton 4 x 4 anti-tank portee

This is the official ‘short term’ vehicle for the 6-pr. Gun, and is now being issued to anti-tank units. There are certain objections to it, of which chief is its large silhouette, which is difficult to conceal. Certain units are at present experimenting with non-basic modifications, in order to reduce the outline of the vehicle. If these are successful, they may be universally adopted.

For the present, however, this vehicle will be used with the 6-pr., because no alternative exists in sufficient quantities.

cheers

Shane Lovell
Canberra, Australia

[Keith Webb]

Generally the 30-cwt versions ran on 16" wheels and the 60-cwt on 20".
There were other differences such as light steering ends and the small steering box on Ford Cab 13 as well.

[David_Hayward (RIP)]

Very interesting information! This is the first documentary info I have seen on the 2-pounder Portees: Chevrolet and Morris-Commercial.

This is a photo of the 2-pounder Chevrolet Portee based on the Chevrolet Gun Tractor which we now accept, I hope, was a 3-tonner chassis although it did not carry a load. This version was officially a 30-cwt. Can anyone confirm please which size wheels they are?

[David_Hayward (RIP)]

This was the ill-fated 6-Pounder Portee based on Chevrolet C60L chassis, although these were rebuilt to 3-tonner G/S trucks. The Chevrolet 2-pouder chassis were rebuilt to G/S lorries, 17-pounder tractors, or sold to the New Zealand Government. I suspect that the 6-pounder tractors were MCC C8/MG Portees, some of which were converted to tractors, others to G/S lorries I think, and some sold to the NZ Government!

[David_Hayward (RIP)]

I do not know the difference myself between the two chassis, but aren't the springs different? The F30 and C30 were initially known as F30S and C60S respectively, suggsting that in the future there would have been lwb versions, but by 1941 this idea must have been dropped and the designations dropped the "S" suffix.

As just mentioned the 6-pounder Portee was rapidly obsolete, although when in production Regina Industries Ltd, a crown corporation based in GM of Canada's former Regina, Saskatchewan plant were occupied with producing 6-pounder guns from scratch. The story makes interesting reading, especially with hindsight and the need for the 17-pounder.

The 2-pounder MCC C8/MG rebuilds included airportable versions, joined in the 17-pounder tractor role with rebuilds of C8/P Predictors. There is a photo of a 17-pounder tractor rebuild of a Chevrolet version in WHEELS & TRACKS suggesting that this was a neat conversion with lower silhouette than the C60L Portee.

[Shane Lovell]

Gentlemen

So what I interpret from your comments is that really there are no external differences between 30 cwt and 3 tonners except the size of the wheels?

David - two points:

1. Overall gist of this section of the artillery notes was finding a suitable tractor for 6 prs and 17 prs. later issues discussed the matter further, but i didn't copy them as I am interested in portees.

2. on the basis of your research, can you differentiate between 30 cwt and 3 tonners by registration number?

cheers

Shane

[David_Hayward (RIP)]

1. Don't forget the differences in chassis lengths: 101" fort he CGT and 2-pounder Portees (I included the CGT here deliberately); 134 1/4" for the F30/F60S, and 134" for the C30 and C60S and of course 158 1/4" for the F60L and 160" for the C60L: although the latter I tend to round up to "160 inches" in everyday parlamce though the F60H 3-ton 6 x 4 had a genuine 160" wheelbase plus that all important 1/4"!

2. I would realy like find out the balance of the comments please as it could be of considerable value.

3. Yes in relation to domestic theatre census numbers and cross-referenced to my database files on Chevrolet and Ford vehicles.

[Alex Blair (RIP)]

Originally posted by David_Hayward
1. Don't forget the differences in chassis lengths: 101" fort he CGT and 2-pounder Portees (I included the CGT here deliberately); 134" for the C/F30 and C60S and of course 160" for the C/F60L.

2. I would realy like find out the balance of the comments please as it could be of considerable value.

3. Yes in relation to domestic theatre census numbers and cross-referenced to my database files on Chevrolet and Ford vehicles.

Hi Dave..
Hate to be pickey but..."and of course 160" for the C/F60L. "..should read 158 1/4"...
Of course an extra inch and three quarters.....forget it..I'm not going there..It's Sunday..

Happy Easter..

[Phil Waterman]

There are a couple of other differences, take a look at the General Specifications and Data pages in the manual as you read down the lines you will see that the following:
• C30 are listed as being 134” WB and there is no 158”WB C60
• Axle track for C30 is ½ narrower then the C60
• Number of springs C30 rear 12 leaves with no auxiliary springs C60 18 leaves with auxiliary
• It also appears that the C30 may not have been equipped with winches while C60 this is a regular option

• There are also some differences between the C60 that are equipped with the 16” rims have smaller brake drums, this I discovered when I went to swap tires and rims between my 1941 Pattern 12 C60L and my 1942 Pattern 13 C60S the brake drums are smaller.

• From the service notes it also appears that the C30 shared the smaller front steering knuckle

[David_Hayward (RIP)]

What is there about that lovely country that makes men pickenickety? Man after mine own heart!

The difference in brake drums traces back to the pre-war period when the requirements for a military chassis that complied with War Office Spec.36A (to E) were being discussed, and it was established that for 16" wheels there was a limit to brake drum size that could be used in connection therewith. What you say makes sense to me having read the hundreds of pages in the files, but may not be obvious otherwise.

The Ford chassis had technically a 1/4" longer wheelbase than the Chevrolet. However I have just noticed that there was a diifference in Chevrolet/GMC chassis wheelbase in the civilian/MCP line: there was a 158 1/4" chassis in the COE 2-ton range, which would have been similar to that of the Chevrolet C60L in theory. The '160"' wheelbase chassis were actually 159 3/4" strictly. How on earth did they quantify that? Ford's clearly thought that their 1/2" made all the difference...oh no I'm going done the same path!

Can anyone confirm the wheel size please on the 2-pounder Portee?

[Keith Webb]

Can anyone confirm the wheel size please on the 2-pounder Portee?

The F60L and C60L 2-pdr portees used 20" wheels.

• There are also some differences between the C60 that are equipped with the 16” rims have smaller brake drums, this I discovered when I went to swap tires and rims between my 1941 Pattern 12 C60L and my 1942 Pattern 13 C60S the brake drums are smaller.

Phil, are you referring to the cab12/13 difference? As far as I know the 6" steering ends with the larger brake drums were introduced with the cab 13. All cab 12s used the 4 7/8" steering ends.

[Phil Waterman]

Hi Keith

"Phil, are you referring to the cab12/13 difference? As far as I know the 6" steering ends with the larger brake drums were introduced with the cab 13. All cab 12s used the 4 7/8" steering ends."

I tried to track down this change over from 5" to 6" steering knuckle when I first got my Pattern 12 and like a lot of things with CMPs the answer is un-clear. Checking the 1944 Parts book it list the brake parts as being listed with the 10:50x16 tires or 10:50x20 tires but when you check the actual knuckle they add a note used after Serial No. 184—28127. So the question now becomes what was the change over date and serial number between Pattern 12 and Pattern 13.

[David_Hayward (RIP)]

Keith, sorry mate, I mean the CGT-based 2-pounder Portees in the photo I posted...16" or 20", as I am no expert.

I had a check of all known 1941 Model Chevrolet CMPs and suggest that the change-over is most likely to have been in amongst C-GT assembly, going by known sequential production numbers.

As to the change-over of cabs, I discussed this in another thread recently:

Changeover Thread

>THUMB SCREW TYPE ENGINE HOODS…BEFORE SERIAL # 084XX04001 AND # 184XX05004 (# 11 CABS) then
ALLIGATOR TYPE HOOD..ON OR AFTER # 084XX04001 AND 184XX05004 TO SERIAL # 284XX01523….(# 12 CABS)
[ also SOLID WINDSCREEN then ADJUSTABLE WINDSCREEN]

I have mentioned before that both Ford and GM of Canada continued 1940 Model production into 1941 to distinguish the 1940 contracts. British contracts placed in late June 1940 went into production arguably before 1941 Model Year had started but was parallel with the 1940 contracts. We also know that 1941 Model production continued after 1942 Model Year started, but for 1943 and 1944 Model Years this arrangement had ceased, though there were no 1945 Models, and all production to the end were 1944 Models! As to when the changeover occurred this must have been sometime in early 1941:

C15A serial # 0844404056, engine # TBA2,816,647 was a # 12 Cab, and 0844403851 engine # TBA2,816,584 was a # 11 cab!
The nearest number I can get to # 184XX5004 is # 1844405023, a C15A! However this could not have been a British order, and must therefore have been a Canadian contract, but with a different serial number system even though assembled possibly the same day or a day later! I can add that by May 1941 # 12 Cab CGTs had arrived in England for assembly, and were in fact assembled at the same time as outstanding # 11 Cab C15s for instance. I just wish I had a definite date!

I have been trying to work out when the # 13 Cabs came in. I have just established that I do not have a definitive answer, and if someone has the information from the parts book please shout! The earliest I can come up with is # 084210006 which is the Pilot C8A HUP, dating to February 1942 albeit with a September 1941 engine. The earliest known 1942 Model was # 284400076, a CGT. However in October 1942 at # 2844513801. the 30-degree opening windshield was changed to a 90-degree one. Gives you some idea of production at the time.

[Keith Webb]

Originally posted by David_Hayward
Keith, sorry mate, I mean the CGT-based 2-pounder Portees in the photo I posted...16" or 20", as I am no expert.

I had a check of all known 1941 Model Chevrolet CMPs and suggest that the change-over is most likely to have been in amongst C-GT assembly, going by known sequential production numbers.

The CGT-based ones all had 10-50-20s.

Here's a pic of the F60L portee restored by John Belfield.

http://www.oldcmp.net/Images/collect...ee/mar07_1.jpg

More...

Here are the remains of one of the Kiwi Portees I photographed in 1986.

[David_Hayward (RIP)]

Cheers Keith! My eyes did not deceive.

[Keith Webb]

Originally posted by David_Hayward
Cheers Keith! My eyes did not deceive.

Yep, your minces are still OK, Daviid.

[Shane Lovell]

David

What is your email and I'll send you the pages. I have moved into the 21st century and now digitally photograph documents. It is easier than transcibing by hand and cheaper than photocopying.

Unfortunately, the document I am using was created in the UK and does not commence until early 1943. You might be interested to know that AWM holds copies of the various artillery notes into 1944/45, just haven't had the time to look at them yet.

What I am yet to find are those produced in the Middle east covering 1941 / 42. I am hoping that these will elaborate further on the development of Portees.

Shane

[David_Hayward (RIP)]

I am astigmatic and myopic. Hence problems seeing fine detail!

Address as always is in the profile but please do send through to:

david@transpenninepublishing.co.uk

Thanks Shane, mate! Your stuff is fantastic! Although these papers and their ilk might be in the UK national archives at Kew, south-west London, they may have been filed somewhere under some obscure reference or they may have never been sent through. I found German bombing photos of Southampton in the NARA, Washington, and nothing in Kew....and lots of info abouth the CMD Southampton in the DND papers in Ottawa!

I should add that I have pre-war information from the DND papers about the development of the standard military vehicle to WD Spec. 36. These papers mention the various types of vehicles covered by the Specifications including "Cavalry Portees", and Morris-Commercial C8 derivatives. The papers therefore mention about Portee bodies and other information and state that drawings of these bodies were sent to Ottawa from 1937. I shall see if I can reciprocate and look through my notes about the subject for you. If I can lay my hands on the Xeroxes of the original papers I might be able to find the copy of the Spec. 36 papers that were placed in the DND file. If I had not seen that file I would never have known that these had ever been drawn up at Woolwich!