French 155mm C mle 1917 Howitzer
with a video by Philtydirtyanimal and a plan by Ken Musgrave

 
The 155mm Howitzer by Schneider, was the principal heavy howitzer piece of the French Army during the Great War. It started as a private enterprise, the design being made by Schneider to get a contract to equip the Russian Imperial Army with artillery. The gun itself proved to be an excellent piece, and when the War broke out in 1914 it was soon accepted by the French Army as well, who needed these types of modern, heavy howitzers - they had put too much faith in their cherished "75". The first model, the mle 1915, employed brass cartridges for the charge, which was seen as a drawback, and a new model, the mle 1917, eventually superceded the first.  

The only difference between the two was some alterations to the Breech. It was a good gun, pretty light (weighing some 1.245 kilos), shooting a 43.5 kilo grenade a maximum range of some 11.500 metres - there were five different types of shells for this gun, including HE, Shrapnel and Gas.

Below is a video of this howitzer in action, courtesy of Philtydirtyanimal:

The plan below comes courtesy of Ken Musgrave (any commercial useage of the plan must first be cleared with mr Musgrave):

The soundness of the design was soon proved by the fact the the Americans adapted it, to equip it's Expeditionary Army in Europe - their copy was called M1917A1. It was still in both French and American service at the outset of the Second World War. (It was also used by a number of other countries, including Finland, who employed the piece with good effect during the Winter War.)

Addition to this article by Wesley Thomas:
The C15S had a swinging loading trough attached to the left side of the cradle. This was a feature that the later C17S lacked. Instead it used a removable loading tray that could be placed on the cradle when loading. Of course the later model had a de Bange pressed asbestos obturation pad on the face of the breech screw for use with bagged charges instead of using brass cases for obturation. Post war Soviet artillery designs (ie: the 122mm M-30 (M-1938) field howitzer, the 122mm A-19 corps gun (M-1931 and M-1931/37) and the 152mm ML-20 gun/howitzer (M-1910/34 and M-1937) all used a Schneider type breech modeled on those of the 105mm L13S field gun (in Russia this was the 107mm M-1910 field gun) and 155mm C15S (or should I say rather, upon the earlier Schneider 152mm M-1910 field howitzer), with separately loading cased ammunition. 

 
The 155mm Howitzer below is currently on display at the excellent Army Museum in Brussels. I examined the paintwork, and it seems to be the original one (French Army Dark Green). Which is consistent with the state of a lot of the other guns, who also sport their original colours.

The photos below were taken by Mark Hansen, at the Australian War Museum in Canberra, whose WW1-collection is among the best in the world, and that contains a number of unique items.

The photos below show the 155mm C mle 1917 that can be seen in the Battlefield Museum in Fleury, Verdun. Notice that this is a modernized version of the gun, with pneumatic wheels.

The photos below (of a gun, dated 1918 on both breach and barrel, and located in a roadside park in Garfield NJ, placed there in 1935 and now in a pretty sorry state) are courtesy of Mike Casale, NJ, USA. Here we can see the US varaint of the gun - save for the wheels, obviously modernized ones. The fourth photo is taken by Philippe Massin, and shows another view of the 155mm that can be seen in the Army Museum in Brussels.

 
Both Cromwell and Skytrex makes smallscale kits of this gun. Cromwell in Resin, Skytrex in White Metal. A very good resin kit has recently been issued by Retrokits.