The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

Handling heavy guns

so annoying to the Union force at Dutch Gap, digging the canal in 1864, did the fire of the Confederate batteries become, that a battery and lookout were established above the canal. The upper photograph shows the big mortars of the battery being placed in position. They are old style 10-inch mortars and very difficult to handle. A lookout with a crow's-nest on top can be seen in the trees. This is where the signal men did their work. During the imprisonment of the Confederate fleet above Chaffin's Bluff, their crews and officers served ashore. So close were the Confederate batteries that with a spy-glass some naval officers actually recognized some of their former companions in the Federal service. That it was no easy task to install this battery is clear from the gigantic paraphernalia to move big guns, shown in the lower photograph. This was a giant sling-cart used by the Federals in removing captured ordnance from the batteries on the James River below Richmond, after there was no more use for the battery shown above. By means of this apparatus the heaviest siege and sea-coast cannon could be moved. The cart was placed over the piece, ropes run under the trunnions and the cascabel, or knob, on the rear of the gun, and a large pole placed in the muzzle for the accommodation of another rope.

Bringing up the mortars at Butler's crow's nest

A sling cart moving a heavy gun