Commander David Dixon Porter, in charge of the Mortar Flotilla, set high expectations for these craft. As with expectations upriver, many thought the 13-inch mortars would rain destruction down upon fortifications blocking passage along the Mississippi. Those championing the heavy mortars figured no defensive work could last more than a few hours against a deliberate bombardment. However detractors wondered if the wooden vessels could withstand the strain.
|Unknown mortar schooner - typical of the type used - note mortar between the masts (Wiki Commons)|
The main armament of the schooners was the relatively new 13-inch naval mortar, identical to the Army's Model 1861 Seacoast Mortar. Fort Pitt Foundry in Pittsburgh, Pennsylvania delivered the first of these in November 1861. Although weighing over 17,000 pounds, the mortar could fire a 227 pound projectile over 4600 yards. Concurrently to production, the Navy built firing platforms to accommodate these massive weapons.
|13-inch Mortar on Navy Platform (Naval Ordnance Instructions)|
|Mortar and platform on an unidentified schooner (Wiki Commons)|
The Mortar Flotilla arrived off the Louisiana coast in March 1862. After reconnaissances, including work by a coastal survey team, Porter carefully placed his schooners downstream of Forts Jackson and St. Philip. Since the schooners were lightly constructed wooden vessels, Porter made sure to keep them out of view and range from most of the Confederate guns. And to prevent accurate indirect fire (as the Confederate garrisons had mortars of their own), the schooners camouflaged their masts with tree limbs. The schooners tied up along the river banks at distances between 2800 and 4500 yards. On April 18, the bombardment commenced at a planned rate of two rounds every minute during daylight hours. On the first day, nearly 3,000 shells landed in and around the forts.
|Mortar schooners in action (from Battles & Leaders)|
Summarizing the employment of mortars, Porter wrote in his official report:
If the efforts of the Mortar Flotilla have not met your expectations in reducing the forts in a shorter time, it must be remembered that great difficulties existed, first, in the soil which allowed the bombs to sink at least 20 feet by measurement before exploding; the difficulty of seeing the fort, as it is not much above the surrounding bushes, and the endurance of the casemates which were deeply covered with earth and better constructed than supposed. But I am firmly of opinion that the moral effect of this bombardment will go far toward clearing all forts of rebels, and I draw attention to the case of Fort Livingston, which held out a flag of truce at the moment three mortar vessels appeared before it.Certainly the mortar schooners failed to perform up to the expectations made by their proponents. However, their detractors were not entirely vindicated. The mortar schooners remained in service, providing support for operations on the Mississippi and with the blockading fleet right up to the end of the war.