Int14200 Col2520
Loading Drill - turret
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Lets look in more detail at what is involved in that simple phrase “1 opens the breech”.

The breech of a 12 inch Mk VI gun weighs nearly a ton (any detailed figures?). It is also not permanently connected to the gun itself.

Behind each gun is an hydraulic power saddle. This is normally in the ‘Reload’ position, as shown. With the gun run in, as would be the case after firing, the front of the saddle and rear of the gun are in close proximity.

To remove the breech, 1 will operate an hydraulic ram which moves the saddle to the right.


As the saddle starts to move, a lever unlocks the breech, then a protrusion on the saddle pushes against a projection on the breech screw. As the saddle moves further to the right, the breech screw is rotated by 30 degrees.

An extractor bar on the saddle mechanism then slides into a slotted lug on the breech screw when the saddle is fully to the right.


A hydraulic ram, parallel to the bore of the gun is then actuated to remove the unlocked breech screw. As the hydraulic ram moves back, it causes the extractor bar to drag the breech screw out of the gun and onto a support tray.

Once the breech screw is fully retracted, the saddle is moved to the left, so that the loading tray is aligned with the bore. At the order “Place the Loading Trays1 rotates a handwheel at the side of the saddle to extend a tray forward and over the threads of the breech. The tray protects the threads from the projectile (weight 714 lbs) and the silk powder bags from the threads.


There is also a need to bridge the gap between the end of the hoist and the rear of the saddle’s loading tray, i.e. through the thick armour at the rear of the turret. It is not clear whether this is formed of a telescopic tray that extends from the rear of the saddle, or from the front of the hoist’s trough, or both. In this illustration I have assumed that the extension comes from within the hoist’s trough.

While the breech is withdrawn, 2 will ream out the vent, which passes through the axis of the breech screw, and will insert a new firing tube [details of firing tube]. This will generally be electrically fired, but friction tubes may be fitted in the event of an electrical failure. [Note that the firing circuit is broken until the breech screw is fully screwed into the gun. A safety switch will only be switched to “On” at the command “Bring both guns to the Ready”, leaving the pistol grip firing lever armed. I would also expect the firing circuits to be broken until the gun is fully run out, but have no evidence of this so far.]


The projectile is then rammed. The main projectiles carried by Colossus were Palliser armour piercing shell, weighing 714 lbs, common shell, or shrapnel.

The powder charges are supplied in hermetically sealed cases (type W) each holding four quarter charges, in silk bags of 73.75 lbs of Prismatic Brown powder.

A full (battering) charge uses all four bags. Reduced charges may only use 3 or 2 charges to reduce wear in the rifling (and cost).

5, 6 and 7 remove the lids from the case before placing it in the hoist’s trough, and the rammer runs through the case, pushing the bags along the loading trays into the gun’s chamber.

With the powder loaded, trays are withdrawn.

Then the saddle is moved to the right to line up the breech screw with the breech, and the hydraulic ram moves forward, rotating drive bars and cog wheels to push the breech screw fully home.

The saddle is then moved to the right, and as it does so, the lug on the breech screw is pushed to the left thereby screwing the breech screw into place. Finally, with the saddle fully to the left a catch engages to lock the breech screw in place.[If not locked in position, the pressure built up within the gun is quite sufficient to push the breech screw to the rear which could turn it the 30 degrees needed to blow it out completely. This could, as they say, ‘ruin your whole day’ if you were in the turret.]


At the order ‘Run Out’, 1 opens hydraulic pressure to the recoil cylinder (which absorbs the recoil momentum of the gun when it fires). The gun moves forward on its slide to the forward position.

Guns are elevated by means an hydraulic ram placed beneath the gun.

The turrets are trained by a pair of hydraulic training engines (for redundancy) that operate via gearing on the outside of the turret.

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(c) Rob.b1904 2008