Why Gun Tractor Shape

[Lang]

I have often wondered why gun tractors have such a weird shape. If there is one thing an artillery tractor needs to do is to carry lots of stuff (not only ammunition but crew gear, tents and all the other gear that Artillery people can not live without).

It seems to me that if they built them with a decent standard back they could almost dispense with the limber which must have driven the crew insane with no reversing ability, completely destroying any cross country ability with 90hp trying to drag not only a gun but a heavy trailer as well, finding parking places for such long combinations would have required extra effort.

It would take much longer to come into action having to deal with two heavy bits of equipment instead of one just getting its ammunition directly out of the back of the tow vehicle.

They obviously found it inefficient as limbers are long gone and it would appear that by the end of WW2 they had been replaced largely by more efficient standard trucks.

Artillery people - Is it just fashion or why?

Lang

[Mike Cecil]

Hi Lang,

I think there was a thread about this subject some time ago that explained the odd shape. Can't locate it now, but I'm sure Hanno can (if my memory is right!)

Aust field artillery tractors parted from the British 'odd shape' by being 'full bodied' (Nos 1,2,3, with rag roof, Nos 8 & 9 with solid body) but still used the artillery trailer until the end of WW2, when only the No.8 & 9 were retained, and the trailer No.27 Mk.1 was dispensed with.

CCKW353 and 'tractors, tracked' were also employed by Australia as field artillery tractors in the latter period of WW2.

The No.8 & 9 tractors were retained into the 1960s being used by the CMF. (Whereas the Regular Army had moved to the GMC CCKW353 and Studebaker US6 as tractors).

Mike

[Bruce Parker (RIP)]

Just a guess but I expect the traversing base for the 18pdr was stowed on the back roof and the slope was to let the gunners manhandle it up there.

[Lang]

Bruce

Could be, but why retain it when the 25 pounders had self-contained rings?


Thanks Mike

When I was a 17 year old kid I was a member of 11 Field Regiment (CMF) in Queensland in 1964. Our battery (at Southport) had GMC's while the rest of the regiment had replaced them with Studebakers.

The GMC's had been in use for many years in our unit. I remember watching them from the classroom window (the Army depot was next door to the primary school) when I was only 13 or 14.

The only Blitz I ever saw on any exercise was a long-wheelbase water tanker from the central transport pool, not a regiment vehicle. I was the 2i/c's driver in a Landrover and remember we had to regulate the speed of the entire GMC/Studebaker/Landrover regiment convoy the whole 300km to Tin Can Bay to cater for the poor old blitz.

A regular Army unit would probably have blasted off as normal and given the Blitz a free-running licence to get there in his own time. At worst they would have put him in the last packet so only a few vehicles had to suffer the pain.

Lang

[David Herbert]

At the start of WW2 they had only just moved on from pulling guns with horses. The limber was there to carry the tools and ammo. The tractor was just to pull it and carry the crew and their kit. It needed to be manoeverable so was as short as possible and easy to hide when the gun was in action. As the war went on the thinking changed and tractor and limber morphed into a full sized truck.

David

[Mike Cecil]

Interesting, Lang. Always good to have first-hand observation.

The Studebaker was the front-line, overseas deployable truck for the regular army from the late 50s (when they were pulled out of storage) until progressively replaced by the No.1 Mk.3 Inter 2.5 ton trucks from the early 1960s.

By 1964, sufficient Studebakers had been replaced in reg units by No.1 Mk3 Inters to see them with CMF units, as you observed. In Victoria, 2 Fd Regt remained with CCKW353 and Tractors No.8 & 9 until the early to mid-60s. Don't remember ever seeing Studebakers with 2 Fd Regt, and as a young lad, I was a frequent visitor (father was BSM, Q Bty) but I may be wrong - it was a long time ago. Studebakers were retained until sold off in the early 1970s. I wrote an article on their Aust use a long time ago, for Army Motors. I think there were about 1,300 in total in Aust service.

Still, that is getting us away from your original question: why the odd shape of the British FAT? (Morris, CMP, Guy, etc)

Mike

[Dan Martel]

Originally Posted by David Herbert

At the start of WW2 they had only just moved on from pulling guns with horses. The limber was there to carry the tools and ammo. The tractor was just to pull it and carry the crew and their kit. It needed to be manoeverable so was as short as possible and easy to hide when the gun was in action. As the war went on the thinking changed and tractor and limber morphed into a full sized truck.

I think Dave has hit the nail on the head. The first tractor-limber-gun set was made to replace the horse-drawn set, and the horse-drawn set didn't carry anything but two members of the gun crew. A tractor could carry the entire crew. A real step forward for the Artillery. Large trucks capable of carrying men, equipment and ammunition were in short supply in the late 30's, and not as capable as they would become later in the war.

The C8 tractor was designed to replace six horses and three riders, and tow the limber and gun, nothing more. The Artillery wasn't looking to make radical leaps in technology at that time, but in a couple years they would be leading the Army in change. and had the trucks to prove it.

Just my 2 pfennings.

Cheers,
Dan.

[Lang]

Apart from the 18 pounder ring theory (later replaced by a spare tyre carrier)
why did they continue to have the strange shape cutting their potential load and usefulness by 50%.

The same number of people were in the crew regardless of horses or trucks. The riders were all gun crew members just like later gun-truck drivers are also just a member of the crew.

The short wheelbase theory does not explain the sloping back as a square box would hold so much more on the same wheelbase.

I am currently of the opinion it is one of those mindless "we have always done it that way" decisions to continue to produce that shape after the traverse ring storage problem had long passed.

Lang

[rob love]

I think Bruce had it right. The early trucks had run flat tires so no need for a spare. The ring for the 25 pounder was not kept on the gun for any long distance...it was stowed on that slanted back. After Burma fell, and rubber became scarce, the vehicles were built without runflats, so needed a spare. At that time the stowage location for the firing platform went onto the top of the limber, and the spare tire location was the slanted backside of the truck.

The move to mechanization was the death of the limber. As mentioned, the limber removed the weight of the gun trail from the backs of the horses. But with mechanization, the towed loads actually need the weight on the hitch for stability. And why not just build a bigger truck so you can carry all the ammunition, tooling, and the gunners kit as well as the gunner? The limber also would have made it a real bitch to back up more than a couple feet.

The Canadians actually built artillery tractors in the early 30s out of locally sourced Leyland trucks. The purpose built DND designed bodies had a large stowage capacity, but the setup still retained the 18 pdr limber. I suspect that when we started building trucks for the British, we ended up following their basic design of the artillery tractor.

[Lang]

Why didn't somebody say "Give us a proper truck so our regiment workshop guys don't need to build racks on the sloping back to carry all the required gear".

[rob love]

They did. From the AEDB Design Records:

"Reports from the field, however, indicated that the 7b2 -FAT did not full-fill all the requirements that had been anticipated, in that the payload was restricted, due to the design of the body. It was decided, therefore, to pilot a new FAT using the same chassis as heretofore, but considerably modifying the body. The sloping after deck was eliminated, and an all steel, open roof body, with superstructure and tarpaulin, was pilotted, the spare tire being housed in a compartment at the rear of the body. Considerably more stowage space was provided, particularly for ammunition which was for either the 17pdr or 25 pdr, role, and more room was available inside the body for the personal and their kits. This was the 7b3 body, and proved to be quite satisfactory."

[Lang]

Well done Rob!

Answers the question.

Lang

[David Herbert]

And of course Morris did the same changes eventually in the UK.

David

[Mike Cecil]

I wonder how much the development and manufacture of the Australian No.8 tractor influenced the Canadian re-design of 1943 to arrive at the 7B3, if at all, or if this was simply independent experience coming up with the same or at least similar result for a common 'problem'?

Certainly the Canadians were conversant with the development of the various Australian bodies for the CMP chassis, as the DME monthly information bulletins were circulated to the UK, Canada, New Zealand, USA and so on (the circulation list is extensive). In the case of the No.8, the pattern was sealed before the end of 1942,and construction orders issued in early 1943.

In profile, the two are very similar except the Canadian body has a 'rag roof' whereas the Australian body is solid steel. There are of course, other differences, such as the spare wheel stowage, but they do have some striking similarities.

The Australians then went on to design the No.9 body with the stepped roof & stowage for the spare wheel (the switch from four run flats to five standard bar treads having been ordered in March 1943.) The No.9 body was considered superior to the No.8, and production contracts of the No.8 were switched to the No.9 in September 1943, after the No.9 had been in production for a few months.

Mike

[Lynn Eades]

On that same line of thought, I wonder who at Ford USA had seen an Australian LP1, When they came up with the higher pitched front armour and shorter drivers front armour (obviously to clear levers)

[chrisgrove]

OK, I'm only a modeller (but with 30 years in the army behind me). Everything I have read says that the sloping back to the various gun tractors were designed to make it easier to decontaminate the vehicles in the case (which seemed quite likely at times) of chemical warfare. Once chemical warfare seemed to be less likely, square back FATs were produced.

In addition, a limber beside the gun was a lot less conspicuous than a gun tractor. If the gun line came under enemy fire, it would seem safer for the gun tractor to be some distance away at the wagon lines and thus less likely to be targetted.
Chris

[Lang]

Chris

My two cents worth is the sloping back/chemical warfare theory does not hold water. The back only makes up about a third of the horizontal surface area and a flat roof would be just as easy to wash down.

Guns can only be inconspicuous until the first shot is fired then they are immediately the subject of counter battery fire. A relatively large percentage of all artillery resources are solely dedicated to this task. If the object is aerial surveillance camouflage before firing then the trucks will certainly be in the hiding plan.

The truck "wagon line" will always be very close (less than 100 metres usually from the guns) if they are not co-located. The driver is a gun-number and must run back from parking the truck when they come into action. If it is open country you may as well leave the trucks behind the guns. If there are a few trees it is wise to take advantage of them.

All the crew gear is also carried in the truck and they must have their living arrangements very close to the guns to come into action within a couple of minutes day or night.

None of this seems to have any bearing on the sloping back design. The 18 pounder ring theory still gets my vote from those offered so far.

Lang

[Owen Evans]

Thought these photos of supposedly prototype Morris and Guy Ant gun tractors might be of interest. Also, the CDSW gun tractor here: http://www.mapleleafup.net/forums/showthread.php?t=6333 also has the sloping back...sort of.

What's the framework on the back of the Guy GT 'prototype'?

Owen.

[Lang]

After 300 years of towing guns maybe the gunners wanted to keep looking at something that resembled a horse's a.....?

[David Herbert]

Just to throw something else into the discussion, quite a lot of modern Humvees have a sloping back. There is no practical reason for it that I know of but at least early on that was the default rear body design.

The two 'prototypes' in post #18 were obviously only intended to be tractors to directly replace horses. The fact that they could easily be used to carry stuff seems to have not yet been noticed.

David

[rob love]

It's almost like they took the guy ant prototype and simply made it bigger. It looks like the rear deck has brackets that are holding legs similar to that used on mortar tripods. I can't place what artillery equipment used those legs.

Re the HHMWVs, they sloping back is on the "slantback" hardtop only. I suspect the slantback was simply so the gunner in the turret ring had an unobstructed view to the rear if he wanted it, or that the hatchback simply gave a little protected cargo room than a flat cargo bed. Kind of the same reason they made car trunks into hatchbacks.

[Ed Landstrom]

To confirm the theory that the sloping back on a Humvee was to give the gunner an unrestricted view to the rear, I was told the same thing by a Humvee driver, so it was what they were being told in training. Specifically, it was designed so that the gunner could fire over the rear with the vehicle parked nose-down on the reverse slope of a berm, using the berm for cover, with the rear of the vehicle facing the enemy. It seems like a rather infrequent use to base a vehicle design on, unless American forward bases are designed with protective berms that would fit this use.

[David Herbert]

Sorry to divert the original point of this thread but I think in the case of the Humvee that the likelyhood of a berm being of a gentle enough slope or just the right height is not great ! I think that Rob's second theory that it was just a way of covering the cargo bed to keep things dry and secure is much more likely, and that similar reasoning was used with the FATs.

David

[Hanno Spoelstra]

Originally Posted by Lang

None of this seems to have any bearing on the sloping back design. The 18 pounder ring theory still gets my vote from those offered so far.

I think this subject is being beaten to death. The sloping back was designed to accommodate the gun's mounting base. Period.

Note: when the design and use of field guns evolved, the design and manufacture of Field Artillery Tractors apparently had to catch up later. Also, don't forget that it is often more effective to keep manufacturing a proven design, rather than disrupt mass production of an otherwise adequate vehicle. This is what helped to win the war: while the Germans were designing new tanks, the North American arsenal of democracy mass-produced an adequate medium tank.

HTH,
Hanno

[David Herbert]

A Sherman has a sloping back too.....

David

[Lynn Eades]

....And you know why, David. A completely different reason to the FAT, Hummer etc.

[Richard Scott]

Originally Posted by rob love

I think Bruce had it right. The early trucks had run flat tires so no need for a spare. The ring for the 25 pounder was not kept on the gun for any long distance...it was stowed on that slanted back. After Burma fell, and rubber became scarce, the vehicles were built without runflats, so needed a spare. At that time the stowage location for the firing platform went onto the top of the limber, and the spare tire location was the slanted backside of the truck.

The move to mechanization was the death of the limber. As mentioned, the limber removed the weight of the gun trail from the backs of the horses. But with mechanization, the towed loads actually need the weight on the hitch for stability. And why not just build a bigger truck so you can carry all the ammunition, tooling, and the gunners kit as well as the gunner? The limber also would have made it a real bitch to back up more than a couple feet.

The Canadians actually built artillery tractors in the early 30s out of locally sourced Leyland trucks. The purpose built DND designed bodies had a large stowage capacity, but the setup still retained the 18 pdr limber. I suspect that when we started building trucks for the British, we ended up following their basic design of the artillery tractor.

I have some memory that the odd Shape was for the ease of chemical decontamination?

[Richard Scott]

https://www.awm.gov.au/collection/C2135093

The 'beetle back' pattern was so named because of its distinctive sloping rear section, manufactured between 1938 and 1944. The unique shape was derived from a design to make the vehicle easier to decontaminate in the event of a gas attack. The 'beetle back' Quad is believed to be the only vehicle to employ this design feature.

from Australian War memorial web site

[Lang]

Ah, the origin of the gas decontamination furphy. There are hundreds of misnamed or misidentified photos and objects in the AWM. Mike Cecil would know more than most that a degree in museum or film conservation does not a military expert make.

Apart from the fact the sloping back made almost no difference to any washing with 2/3 of the upper surface still horizontal, a division might have 3,000 vehicles but the only ones they wanted to wash down easily were 100 gun tractors?

Lang

[Hanno Spoelstra]

To add to the confusion, some sources state the "The Canadian Chevrolet CGT Artillery Tractor came with both a fully armored cabin and a partly armored one"

Hope the confusion is complete now!

H.