War of the Rebellion: Serial 046 Page 0319 Chapter XL. OPERATIONS ON MORRIS ISLAND, S. C.

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NOTE Numbers 11.

MORTAR PLATFORMS.

The siege mortar platforms of Batteries O'Rorke and Weed, used in the first bombardment of Fort Wagner, and those of Battery Totten, used in the bombardment of Fort Pulaski, April 10 and 12, 1862, all showed evidences of failing, and required important repairs after a few hours' firing. These platforms were made of the deck plank, 9 feet long by 5 inches by 3 1/2 inches, furnished by the U. S. Ordnance Department, and were put down in conformity with the rules from laying these platforms, given in Heavy Artillery Tactics, pages 91 and 92, modified slightly by circumstances uncontrollable in field operations.

I sought a mortar platform for direct firing which should be more durable than the above noted, and such that there could be used in its construction the heavy squared timber and plank captured on Morris Island. The simple one shown in Fig. 18 [p. 320] was made and put down for the 10-inch siege mortars in Battery Weed, and a similar one for the 8-inch mortar of Battery Reynolds, July 21, the only difference being in the width from center to center of the rails; in the 10-inch it is 28 inches, in the 8-inch 22 inches. The material was yellow pine. The 2-inch plank forming the foundation were thoroughly spiked fast to the rails. The platform is bedded with the vertical plank to the rear, and buried so that the upper surface of the rails is level with the terre-plein of the battery. No pickets were driven to stay it.

These platforms were used throughout the siege, with very slight repairs. Those for the 8-inch mortars were moved with the pieces from the first to the third, thence to the fifth, parallel. More than 500 rounds were fired from each, at ranges of from 200 to 1,300 yards.

Fig. 19 [p. 320] represents the platforms laid for the 10-inch sea-coast mortars of the battery at the Beacon House, never used. If the decking in this last plan had been extended over the whole platform, a mortar could be fired in any direction from it. In a similar manner, i. e., be means of a decking, the rail siege platforms above described could be prepared for general firing.

The following rules relating to the construction and use of mortar platforms embody many of the facts observed in the siege of Fort Pulaski and Wagner, the supporting earth being a fine quartz sand.

1. It is indispensable that the parts comprising the platforms be thoroughly fastened together by means of joints and spikes or screw bolts. The latter should be used for very long ranges.

2. The plan of the platform may be varied somewhat to suit the material at hand, the amount, range, and direction of the fire. Large constituent pieces are best. For siege mortars, a platform containing 20 cubic feet of lumber, and having a bearing on the ground of 36 square feet, is safe for average circumstances. Thirty cubic feet and 54 square feet would be correspondingly safe for seacoast mortars. For direct firing the platforms should be longest in the direction of the line of fire.

3. Pickets driven about platforms will not prevent them from being forced to the rear by long-continued firing.

4. The greater the weight of the mortar in proportion to the weight of its shell, the less the injury to the platforms; hence the new pattern mortars are least destructive.