Gunner's Sight and Level

Gunner's sights and levels are found either separately or combined together in composite instruments. They were intended to be set up on the barrels of large guns so that gunners could aim at their target and elevate the gun to the correct angle for the estimated range.

As with other artillery instruments, sights and levels were introduced in the 16th century. They were intended to accompany the new form of cast bronze guns which came into increasing use from the late 15th century. This new style of artillery could be set at variable elevation: pivoting around its trunnions, the gun could be placed at an angle determined by the master gunner.

To achieve maximum destructive force, most cannon were in practice fired at point blank range, for which the gun remained horizontal. But after Niccolo Tartaglia's La nova scientia (1537) - the first published work on the 'new science' of artillery and ballistics - there was much discussion of the increased range that could be obtained by elevating the gun.

The gunner's level enabled the elevation of a gun to be measured. Like the gunner's quadrant, a plumb bob provides a reading against a scale. However, whereas the gunner's quadrant is inserted into the mouth of the gun - exposing its user to enemy fire - the level is set up more safely at the breech end of the barrel.

The instrument came in a variety of forms, with a degree or a tangent scale graduated either on an arc or a straight rule. Most surviving devices have a rigid plumb bob rather than a thread. Despite the diversity of their designs, all such levels are used in the same way and are set up along the longitudinal axis of the gun.

In its most basic form a gunner's sight is simply a mark or prominence by which the gunner could visually align the gun with a target. In its instrumental form, the sight performed an additional task; like the level, it was used to set the gun's elevation.

The sight is placed at the breech end of the gun and the target viewed through a pinhole, so that the target, the upper edge of the gun's muzzle and the pinhole are all in line. The greater the elevation, the higher must be the pinhole above the breach. The elevation is recorded as the vertical height of the pinhole, usually graduated on the instrument in inches.

The gunner's sight appears in two principal variants in which the sighting holes are either fixed or sliding. In the fixed form there are several pinholes arranged in a vertical line at equal intervals. The sliding version provides greater flexibility since it has a single pinhole in a sliding piece which moves against a scale.

One of the earliest texts to discuss gunner's sights and levels, Vanoccio Biringuccio's De la pirotechnia (1540), concludes its account by remarking that although such 'instruments aid greatly, they are not essential'. Many surviving instruments seem to bear this out. They are often finely engraved and gilded devices, apparently intended more for noble patrons than for service on the battlefield.

Stephen Johnston
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