The advantages of this type of gun was the protection afforded to the detachment as well as its initial concealment until the first shot was fired. These minor advantages were far outweighed by the serious disadvantage of its slow rate of fire. An excellent gun crew could get off about one shot a minute. Most of this time was taken up moving and positioning the gun. Other disadvantages were its weightiness, and the consequent difficulties in handling and maintenance.
The gun piece and its disappearing carriage were supported on roller racers mounted on a circular track embedded in the concrete floor of the emplacement. Two calibers were used in New Zealand, 6-inch and 8-inch. The carriages they used were almost identical, the main difference being size and weight. Five of these remain in one piece. Two in Auckland, two in Lyttelton, and one in Dunedin (they are all in various different states of preservation).
