24 replies to this topic

[Ewan Johnstone]

Can any RFA or field gun experts help me identify the type of gun being used in the attached picture? To my shame as an ex gunner I have simply no idea.


    Your's Aye

  Ewan

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[Ewan Johnstone]

Edit to my original, I am aware this picture is between the war's, and any help is appreciated.

[munster]

I think it is a 15pd the barrel is above recoil bits n bobs as you can tell by the expert description i is no expert but was looking at pictures a few days ago.john

[MikB]

18 pounder Mk.IV? Later than the classic Mk.II.

[Ewan Johnstone]

Thanks chaps

[nigelfe]

18-pr Mk IV on Mk IV Carriage

[Stoppage Drill]

Obviously Australian artillery.

[Old Tom]

I wondered what post 7 meant; that was before I looked at the picture. However to expand the topic, may I ask why the change in position of ordnance and recoil system. I was aware that WW1 field guns had ordnance below recoil and that the later 25 pdr was the other way. I was not aware that some later marks of 18 pdr had changed. I supose that its a question of the height of the trunnions in relation to the carriage and perhaps ordnance over recoil allows greater elevation. Can an expert confirm and expand please?

Old Tom

[centurion]

A bigger restriction on elevation was the use of the pole trail. This was removed on the 25 pounder with the use of  a box trail that allowed the equipment to be used in both gun and howitzer role. Subsequently the split trail has been the answer.

[MikB]

Mk.III and IV carriages appear to've used a box trail with a big enough aperture to allow much higher elevation, and the Mk.V carriage a split trail with IIRC 25 degrees side traverse.

There doesn't appear any particular advantage in putting the boreline over the recoil system - it would be interesting to hear of any engineering considerations. Many systems, for example the US 105 and the German 88, divided the system between buffer and recuperator above and below the bore.

Regards,
MikB

[CharlieBris]

Krupp and Rheinmetall explored the positions of trunnions, recoil/recuperator assemblies in 15cm and 21cm howitzers before WW1. The main problem was to keep the howitzer weight
down to a max. of 2.1t - the German Army max. for horse towed field artillery. A box trail could permit high elevation angles but the breech disappeared into the trail at high elevations
and the gun had to be brought back towards 0 deg elevation to reload (e.g the 15cm sFH 02). The Krupp solution was to use rear-mounted trunnions with equilibrators so the breech stayed in the same position with respect to the carriage regardless of the elevation. The Krupp 21cm Morser and  15cm prototypes had the recoil/recuperator above the barrel presumably to lower the C.G. of the gun and (possibly) to reduce flexing of the barrel on firing. British and French artillery experts were quite dismissive of the Krupp scheme at the time (around 1910) saying the rear mounted trunnions would give unacceptable variation in shots due to vibration and flexing of the barrel. (more on the 21cm at http://www.ammsbrisb...L0=7&L1=1&L2=33, the 15cm prototypes at http://landships/lan...hsHaubitze.html

As it turned out the 15cm German howitzer used in WW1 was a mixture of Krupp and Rheinmetall designs but it did retain the rear-mounted trunnions with an under barrel variable recoil system.

The best example I can think of a split trail carriage is the French 155mm GPF - had 40 deg traverse although it needed a hole dug in the ground behind the breech to fire at high elevations.

Regards,

Charlie

[nigelfe]

18-pr Mk 4 carriage was box trail, Mk V was split trail.  Trials with 25-pr Mk 1 on 18-pr carriage concluded box trail was better (although with 25-pr Mk 1 both were used due to shortages).  Box is better because it means the trails are shorter, hence lighter, to achieve the same degree of stability compared to split.  I won't try and explain this without a diagram.  It's also much better for direct fire and isn't disadvantaged for wide traverse providing the gun is properly balanced so one man can traverse it.

[centurion]

The reason for moving the recoil mechanism from above the tube to below was to increase stability. The trunions were fixed on a trough cradle (the rectangular box below the barrel) in which the recoil cylinders were placed. The recoil piston rods were fastened to one end of the cradle. The pistons went back with the barrel when the gun recoiled. This allowed a longer and smoother recoil action which was further improved when an automatic compensator was fitted to the Mk IV gun. This varied the recoil length according to factors such as elevation and avoided 'jumping' at higher elevations. The greater stability allowed a higher rate of fire. It also allowed the Mk IV carriage to be fitted on a traversing wheel making it more suited for anti tank work (it should be remembered that it had been expected that the German response to British deployment of tanks en masse would be the production and deployment of large numbers of tanks). The recoil system, box trail and traversing wheel all became features of the 25 pounder (which was on occasion used in an anti tank role).

[MikB]

centurion, on 22 June 2012 - 11:44 AM, said:

The reason for moving the recoil mechanism from above the tube to below was to increase stability. The trunions were fixed on a trough cradle (the rectangular box below the barrel) in which the recoil cylinders were placed. The recoil piston rods were fastened to one end of the cradle. The pistons went back with the barrel when the gun recoiled. This allowed a longer and smoother recoil action which was further improved when an automatic compensator was fitted to the Mk IV gun. This varied the recoil length according to factors such as elevation and avoided 'jumping' at higher elevations. The greater stability allowed a higher rate of fire. It also allowed the Mk IV carriage to be fitted on a traversing wheel making it more suited for anti tank work (it should be remembered that it had been expected that the German response to British deployment of tanks en masse would be the production and deployment of large numbers of tanks). The recoil system, box trail and traversing wheel all became features of the 25 pounder (which was on occasion used in an anti tank role).

I can see some of those arguments, but it still begs the question of why Uncle Sam and Jerry both went for divided recoil systems in the high angle guns I mentioned. I'm wondering if the compensator was actually most effective at low elevations where a longer stroke would reduce the upward couple of the rearward horizontal force applied well above the trail spade's centre of resistance. Since the US 105 and German 88 were designed for HA use, that particular issue would at the design stage have seemed less significant. Despite the 88's feared reputation at low elevations in plain and A/T roles, footage of the thing shooting shows that the recoil at these elevations was pretty disturbing to the mounting.

Regards,
MikB

[centurion]

Somewhat irrelevant to field guns I think

[MikB]

centurion, on 22 June 2012 - 12:20 PM, said:

Somewhat irrelevant to field guns I think

I don't think so.

The multiple roles into which the later 25-pounder, US 105 and German 88 were going to have to fit were already beginning to develop at the end of WW1. The field gun was becoming a more general-purpose beast.


Regards,
MikB

[Old Tom]

I am not convinced that the issue has been addressed yet. Types of trail are not, I think, relevant;  the transition from pole to box to split  seems to have been driven by changes in traction and the need for elevation to allow indirect fire. Stability presumably improves if the heaviest part of the equipment i.e. the ordnance is as low as possible, and this would seem to favour the 13/18 pr configuration with recoil above barrel, but, I think, there is not a lot of difference. The French 75mm was very stable and was capable of a high rate of fire. The ordnance was above the recoil system (hope that's right) but stability was due to the effective recoil system and I believe to the device which anchored the carriage by being positioned between the wheels and the ground. In principle a little like the 25 pdr.

Old Tom

[centurion]

MikB, on 22 June 2012 - 02:28 PM, said:

I don't think so.

The multiple roles into which the later 25-pounder, US 105 and German 88 were going to have to fit were already beginning to develop at the end of WW1. The field gun was becoming a more general-purpose beast.


Regards,

MikB

The thread was about field guns - if you want to discuss WW2 weapons in detail I suggest elsewhere

[MikB]

centurion, on 22 June 2012 - 05:28 PM, said:

The thread was about field guns - if you want to discuss WW2 weapons in detail I suggest elsewhere

My point was that part of the motivation for the design change might have been the recognition that the role of the field gun was changing, and that some other guns not originally conceived as field guns effectively became so. I didn't and wouldn't go into specific detail of WW2 weapons, but history is a continuous process, not episodic chunks.

Regards,
MikB

[nigelfe]

centurion, on 22 June 2012 - 11:44 AM, said:

The reason for moving the recoil mechanism from above the tube to below was to increase stability. The trunions were fixed on a trough cradle (the rectangular box below the barrel) in which the recoil cylinders were placed. The recoil piston rods were fastened to one end of the cradle. The pistons went back with the barrel when the gun recoiled. This allowed a longer and smoother recoil action which was further improved when an automatic compensator was fitted to the Mk IV gun. This varied the recoil length according to factors such as elevation and avoided 'jumping' at higher elevations. The greater stability allowed a higher rate of fire. It also allowed the Mk IV carriage to be fitted on a traversing wheel making it more suited for anti tank work (it should be remembered that it had been expected that the German response to British deployment of tanks en masse would be the production and deployment of large numbers of tanks). The recoil system, box trail and traversing wheel all became features of the 25 pounder (which was on occasion used in an anti tank role).

Eh, wrong not entirely correct.

I suggest looking at the carriage stability section and Figure 7 on this page of my web site http://nigelef.tripod.com/gunchars.htm

As far as height goes the lower the trunnions the better stability is.  As my figure 7 shows stability is about vertical and horizontal mechanical forces, the smootheness or otherwise of recoil has little or nothing to do with it.  Cut-off gear was used to reduce recoil length as elevation angle increased, this was a virtuous circle because recoil length had to to be shortened to prevent the breach hitting the ground with increasing elevation angles, but with increasing elevation more of the recoil force went downwards.  Of course in WW1 with large wheels for equine (and engine) traction the stability problem was worse that later when smaller diameter wheels were introduced for mechanical traction (and made cut-off gear important).

Incidentally 25-pr had a 'platform' not a 'traversing wheel' (which is what the layer uses).

[MikB]

nigelfe, on 23 June 2012 - 06:23 AM, said:

As my figure 7 shows stability is about vertical and horizontal mechanical forces, the smootheness or otherwise of recoil has little or nothing to do with it.  

I would suggest it does. Although the avoidance of potato-digging with the breech at high elevations is important, avoidance of jump at low elevations is significant too in a multirole gun. In order to minimise the backward force close to the horizontal and reduce the couple that's trying to lift the wheels and rotate backward around the trail's dig-in point, the recoil stroke at low elevations should be long, to extend it over time. If it isn't smooth(ish), there'll be spots where the force increases and the advantage of the long stroke will be - at least partially - lost.

Regards,
MikB

[nigelfe]

Jump is a different matter altogether, although carriage and barrel jump are usually combined to give a single figure, usually a few minutes/mils, and allowed for in the ballistic calculations.  You'll find it on the first page for each charge in the Range Tables.

However, I suspect you don't mean jump :-)

I haven't a clue what is meant by smoothe recoil.  I find the concept of ragged recoil meaningless and don't see how it can occur in a hydro-pneumatic system (or springs for that matter). The nature of a recoil system is that it smoothly absorbs the recoil forces and increases resistance as the full recoil is approached to prevent the piston, etc, from banging against stops - that would be ragged.

What the cut-off gear does is allow maximum recoil length at low elevation, gradually reducing recoil length as elevation increases.  However, I'm not actually sure that any UK WW1 hows had cut-off gear.  Obviously it was unncessary for guns with their limited max elevation.

Given that guns like 13, 18-pr, 4.5H were designed to have the layer in the seat during firing then obviously there wasn't much of a problem with the gun bouncing around.  Ie it was stable because the carriage dimensions were correct for the recoil force.

[Old Tom]

One might interpret the last sentence of post 22 as indicating that the relative position of ordnance and recoil system had no effect on stability. If that is the case the choice of the arrangement was up to the designer and hence the trend to allow greater elevation of field guns could have been the motivation.

Old Tom

[CharlieBris]

There is some evidence for how much the WW1 guns jumped around on firing. There are a number of film clips on YouTube from WW1 of various guns being fired.
In general, the light field guns don't seem to show much evidence of jumping. The French 75mm Mle 1897 looks particularly stable when fired.

There are some guns of the period which seem to show a lot of jumping around - one I can think of is the British 6 inch gun. This was a 6 inch Naval gun stuck on
a wheeled carriage. It appears that the original recoil system wasn't upgraded. Naval recoil systems weren't, I think, designed for full recoil absorption but to reduce the
recoil forces down to a safe level which could be absorbed by the mounting and structure of the ship. On wheeled carriages this meant the gun would jump on firing
and the carriage roll back. One clip shows the gunner snatching the gun sight off the gun before firing presumably to prevent damage to the gun sight.

Some of these clips are linked off the Landships II website artillery section.

- clip of 6 inch firing and a 21cm Morser plus a bunch of old siege artillery

Regards,

Charlie

[nigelfe]

Old Tom, on 24 June 2012 - 10:50 AM, said:

One might interpret the last sentence of post 22 as indicating that the relative position of ordnance and recoil system had no effect on stability. If that is the case the choice of the arrangement was up to the designer and hence the trend to allow greater elevation of field guns could have been the motivation.

Yes, the relevant issue is trunnion height, the lower the better, of course that creates recoil problems at higher elevation, one solution being to mount the trunnions as far back as possible on the elevating mass.