"British bridge classification of Sherman tanks" Topic

I asked this over on WW2talk but didn't get a definitive answer, so thought I'd try here as well.

I was looking at the info on bridge classifications for British Army vehicles recently, and found myself confused by a particular point (no real surprise as military bridging is not one of my strengths!).

MTP No.74 (supplement on "A" vehicles") of Mar 1944, and MTP No.74 of Sep 1945 both list all marks of Sherman with a classification of 33, which rises to 35 for the Vc. The RE Reconnaissance Pocket Book states that an Armoured Division needs both Class 9 and Class 30 bridges.

If I'm understanding it correctly though, a Sherman with a classification of 33 should not attempt to cross a Class 30 bridge. The Divisional Bridging Troop (or Platoon) carried sufficient Bailey equipment to build a Class 40 bridge of 80-foot, so in that respect could accommodate tanks of up to (and I presume including?) 40 classification anyway.

I had a quick look in Bellanger's British Soldier, as I recalled it has a section on markings, and he shows all Shermans with a bridge classification plate of 30.

Any thoughts on what appears to be a discrepancy in the available figures?

Gary

Having brought the subject up, I had a quick survey of my sources. My model Shermans have a '33' class marking and I have seen contemporary illustrations showing this. Also, as far as I can make out, '33' was the official British classification for Shermans. So far, so good. However, it does not take long to produce illustrations, both modern and contemporary, which show a classification of '30'. It cannot just be the British Army being the British Army so I wonder if the '30' was an early classification which was then officially replaced or 'updated' but putting on the new signs took time. Anyone else have some information or can point to a source?

Tanks can cross a bridge that has a slighly lower tonnage classifiaction by 1) driving slowly and 2) having only one tank on the bridge at a time. That was what I learned while in the US Army in Germany during the 1970s and 1980s. I can't recall the "formula" for computing the tonnage vs carrying capacity however.

Jim

What Jim said.
Usually engineers ate bridges at levels a bit less than what will actually stress them out as. Sometimes by anywhere up to a quarter to even a third. Ebgineers will play it safe and fudge the safety factor just about every time.

Those "9" and "30" classifications are to cover the scales found in most vehicles in a reconnaisance regimetn in the UK. It will cover just about anything up to either half track or armoured car and thirty to cover all the tanks. The only outlier was when the Staghound was involved as a 15T armoured behemoth.

Also note that the UK had recconnaissance regiments composed of armoured cars and other reconnaissance reegiments of tanks that were identical to a tank regiment.

Here is a paper on the formulas: PDF link

Wolfhag

As far as engineering safety factors, a quarter or a third is a bit risky.

I remember a line about a mathematician, a builder and an engineer being asked what is Pi.

Mathematician: "A transcendental number, approximately 3.14159, represented by the symbol π, that expresses the ratio of the circumference to the diameter of a circle.

Builder: Approximately 22/7

Engineer: A bit more than 3 but let's call it 10 to be on the safe side.

Hi Gary,

I used to be a RE reserve officer. Unfortunately I don't have access to any of the documents any more (PAMS – not sure if they were called that back in the '40s).

Both the GSB and LSB (the modern Bailey) have markedly different classifications for one vehicle at a time compared to continuous traffic. The calculation of this is a bit more involved and isn't in PAMS. The standard meaning of bridging load is for continuous traffic of the maximum vehicle load at convoy speed and spacing. There are many photo examples of Baileys, some with "one at a time signs", some without which I hope is evidence of this.

The only reference to this I can find online is this US manual where there's a short reference to it – Chapter 5, section VI (page 65)
link

Having said that, I suspect the real reason might be more likely to be the standard bridging classifications having the nearest round number being 30.

I hope this is helpful. I'm an engineer (very rusty) in civilian life too so would be happy to attempt more technical detail if it would be useful.

Peter

I thought I had some notes on this somewhere but alas…

Having a quick poke around it seems '33' is the number usually seen but I notice a significant difference in the combat/operational weight of some of the later Shermans compared with their earlier brothers. Eg some data plates here:
link

The only discussion of the '30' vs '33' question I came across was here, with the same explanation and some further (unsourced) comparative data:
link

Thanks for all the above responses and pointers for further info. So taking all the above into account, it does seem there was an evolution of weight involved that had a knock effect to the bridge classifications. A British summary from 1942 had the Sherman as approximately 30-tons (British long) so a bridge classification of 30 would be expected. Later models then creep up, from around 66,500-lbs (Sherman I) to 69,000-lbs (Sherman III) and 71,000-lbs (Sherman V), at least as given in the US Ordnance Items catalogue.

The earliest British document I've seen for bridge classifications of vehicles is early 1944, by which time the later, heavier models are coming into British usage. Possibly then, the older stock painted up as '30' was left as such, with the newer Vs and Vcs getting the higher numbers of '33' and '35' respectively.

I must admit while it was mentioned on WW2talk I hadn't considered vehicle spacing. Military Training Pamphlet No.74 (the period PAM on the subject) states that standard spacing should be maintained at 50 yards (150-foot) between vehicles in convoy, and should never be closed to less than 80-foot. That would certainly mean an 80-foot Bailey put up by an Armoured Division should only expect the 'one at a time' mentioned above.

The figures I've seen re Bailey bridging equipment in particular, as carried by Divisions and RASC Bailey Platoons, do all centre on constructing a Class 40 bridge, which should have been able to handle Shermans, Cromwells, Comets and Churchills alike.

Gary