The military value of a 21cm howitzer (Mörser) had been apparent to the German Army from the Franco-Prussian war of 1870-71. The first crude bronze 15 ton 21cm howitzer was used in the siege of Strasbourg. There was a requirement raised in 1902 to replace the 21cm Krupp 1899 mörser with a gun with recoil/recuperator. The first two Krupp prototypes Nr.1 and Nr.2 were rejected. The third prototype (Nr.3) was promising enough for an order of 8 guns (two batteries) to be placed in 1906. This Versuchsmörser was considered generally satisfactory except that the max. range was too short. The Mörser was fitted with removable track pads with 10 wooden plates for each wheel to prevent the gun from sinking into the ground. The weight of the gun was too large to be moved as single horse drawn load so a 4 wheeled trailer was used to transport the barrel of the gun.

Calibre	21.1cm L/10
Weight of Gun (emplaced)	5384kg + 750kg (trackpads)
Type of undercarriage:	Räderlafette mit Rohrrücklauf
Max. Range	7000 m
Shell Weight	112 kg
Elevation	-4° to +60°
No. Built	8

The findings from testing of the Krupp 21cm Versuchsmörser Nr.3 M1906 were incorporated in the design of the M1910 Mörser. It should be noted that Rheinmetall produced prototype 21cm Mörsers in 1907 and 1912 but neither of these were accepted for production.
The two batteries of Versuchsmörser were used on the Western front in late 1914 or early 1915 when the need for artillery pieces far outstripped the number of guns the active and reserve batteries held or the industry could supply. One of the 21cm Versuchsmörser Nr.3 (serial #5) survived the war and was given to Australian forces from the pool of surrendered guns. This gun has survived and is displayed at Barclay Square, Red Cliffs, Victoria. (-34.307464,142.187357 Google Maps)

Images courtesy of "easo" MVCA forum

An image of this Mörser has turned up and visually it's the same gun. However, the Recliffs Mörser seems to have an interrupted screw breech block whereas the one in the image clearly has a sliding wedge breech. Perhaps, and this is speculation, that part of evaluation of this Mörser design included testing different breech designs.

References for 21cm development section
"Das Gerät der schweren Artillerie", Generalleutnant a.D. H. Schirmer, Verlag Bernard & Graeffe, Berlin 1937, Page 92-95.
"War Trophies From the First World War", Major R.S. Billett, Simon & Schuster Australia, 1999.p.57
"Die schweren Geschütze der Welt", F. Kosar, Motor Buch Verlag, Stuttgart 2002, Page 57.
"German Artillery of World War 1", Herbert Jäger, Crowwod Press 2001, Pages 36,38.

When the War started in 1914, the German Army could field 216 of these big guns, and they were used from the very first days of combat. When the Germans came upon the strong Belgian fortress of Liège, it was these guns that started the attack on August 5th, by sucessfully shelling the forts in the Eastern perimeter, and eventually paving the way for the REALLY big guns, the 42cm Dicke Berthas. It was then used with effect on all fronts, primarily in the Regiments of the Fuss-Artillerie, as one of the standard weapons of indirect fire and support. The Foot Artillery Regiments - a Corps asset - were the primary units of the heavy German Artillery, each containing two batallions of four batteries each, were the main equipment was 15cm guns. Howitzer Battallions however, had only two batteries per batallion. The number of guns per battery varied between 3 and 4. In a quiet sector, a Division had some 8-9 batteries of 15cm and 21 cm guns in support, but normally some 16 batteries were employed per division.

Experience from the fighting soon made the Artillery men realize that an increase in range would be most helpful, as the comparatively short range of the Howitzer often forced the units to site their guns well within range of most enemy artillery. A small redesign followed: the gun barrel was lengthened somewhat, from L/12 to L/14.5.

This new variant was called m/16 or Langer Mörser. However, as the gun already was pretty heavy and cumbersome, the redesign had been done from the premiss that the weight should not be increased. That was pretty much adhered to, but with the effect that the increase in range was even less than one kilometer. Another small redesign, following combat experiences, was the fitting of a Shield. (Some m/10 were retrofitted with this, but not all.) When the war came to an end in 1918, the 21 cm Howitzers of the German Army had fired some 7 million shells.

The video below, courtesy of PDA, shows the Mörser in action:

Calibre	211 mm
Weight of Gun	15.49 (m.10) 17.53 (m.16)
Max. Range	9.4 km (m.10) 10.2 km (m.16)
Muzzle Velocity	225-394 m/sec
Min./Max. Elevation	+6°/+70°
Shell Weight	121 kg

The plans below have been made by Ken Musgrave and are his copyright. Any commercial use of them can only be made after an agreement has been made with Mr Musgrave.

Captions will appear with the expanded image

Dug in Howitzer, with full crew present - including the Platoon commander in light coat - while shifting the tail of the gun. The gun layer supervising the whole operation. Most men on the left of the trail are obviously trying to get the second, foldable earth-spade clear of the ground

Howitzer firing, at full recoil. Obviously a hurried grouping of the gun: no concealment or earth works to be seen. Point of interest: the gunner pulling the lanyard.

A rather blurry photo, I’m afraid, but interesting as it shows a mixture of guns both with and without shield. Note also the fanciful camouflage scheme on the gun nearest to the camera. Note also the limbers, with seating for the crew.

A gun being loaded: four men working the Loading Cradle, one man pushing the projectile into the breech. Note the camouflage netting above the Gun Pit.

A Howitzer Model 16 "Langer" - notice the Extra Length of the Barrel. Taken in Flanders (or Artois), and obviously in rather close proximity to the Fighting: notice the devastation and the maximum elevation of the Gun Barrel. Note also the camouflage of the Gun: nice example of a Buntfarben-scheme. If I would hazard I guess, I would say that the base colour is Dark Greenish, with spots of Lighter Brown and Sand.

Dug in Howitzer firing, probably the same as seen above. The rear, fixed Earth Spade is not used, in fact the whole trail is up in the air: they are obviously relaying on the foldable Earth. (It could also be a so called Siting Shot, where the Spade is forced into the ground by the Recoil.)

Here the Gun is broken down, in anticipation of regrouping. The Barrel is separated from the rest of the Gun, and dragged away on its own Wagon. The photo was taken at Estaires, during the Battle of Armantieres.

Another Gun, being either dismantled or put together - judging from the lack of hurry, and the Shelter being built on the left, I would put my guess on the later. Notice the camouflage of the Gun.

Howitzer firing from a well protected position. Notice the stocky Shell waiting on the ground, and its transport casing made of wicker. This photo was taken during 1916, during the Battle of Verdun, in what the Germans called the Küchenschlucht. The Howitzer belonged to the 1st Bayerische Fussartillerie-Regiment. This Regiment alone lost some 230 Guns at Verdun!

Another scene from the terrible Battle of Verdun, taken near Besancourt.

A gun being adjusted. The photo was taken during the Fighting in Romania, at Sereth.

Photo from the Early part of the War. Notice the teams of oxen being used as draught animals. Fuss-Artillerie indeed: No Blitz-Krieg here!

A gun being prepared for action, the branches used for concealment have just been removed. All work has been done by the book: the tools and equipment belonging to the gun to the left, shells and gunners waiting a bit off to the right, the wheels of the gun resting on some sort of mat. This photo was taken on the Sereth front in Romania during the Summer of 1917.

A 21 cm participating in the shelling of the Fortress town of Przemysl in Galicia, after it had been taken by the Russians.

A 21 cm mörser being adjusted by the aimer. Photo taken on the Western Front. Exactly where is unknown.

Same gun as to the left. Now it’s being loaded. The obvious lack of urgency points towards this being another posed photo.

A gun well positioned, with dug-in for the crew on the right. A shell is resting on the Loading Cradle, but as the gun is steadily pointing towards the sky, and as there is neither any Gun Layer nor any one ready to push the shell into the breech, this is obviously a staged photo.

There is a highly detailed walkaround of a 21cm Mörser at Childers, Queensland on the AMMS Brisbane website.

The location of the following is not known but Peter suspected that the colour is the original German paint, showing yet another variant of the so called Feldgrau colour, this time the shade called Reseda-Grün.

21cm Mörser at the Army Museum in Brussels. (Photos courtesy of Philippe Massin!) Here you can see the gun in a sort of semi-limbered state, with the barrel wagon in position to maneuver the barrel in place. Notice that this gun is equipped with the shield.

21cm Mörser can be seen in the A6 Military Museum in Jonkoping, Sweden: