Porter's mortar schooners - failure to meet expectations

Earlier we looked at the Mississippi River mortar boats used upriver at points such as Island No. 10 and Fort Pillow.  While suitable for the inland rivers, being little more than rafts these were not capable of ocean passage.  For the lower reaches of the Mississippi, the Navy acquired several ocean going civilian vessels to form a "bomb flotilla." 

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)

Porter received twenty schooners outfitted with mortars.  These ships retained their civilian names upon commissioning - USS Adolph Hugel, USS Arletta, USS C.P. Williams, USS Dan Smith, USS George Mangham, USS Henry James, USS John Griffith, USS Maria J. Carlton, USS Matthew Vasser, USS Norfolk Packet, USS Oliver H. Lee, USS Orvetta, USS Para, USS Racer, USS Sara Bruen, USS Sea Foam, USS Sidney C. Jones, USS Sophronia, USS T.A. Ward, and USS William Bacon.  (The barks USS Horace Beals and USS A. Houghton are sometimes cited along with the mortar schooners, but these served as guard and stores ships, respectively). 

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)

Unlike the smaller upriver boats, which might be maneuvered about to adjust the line of fire, the schooners required some means to traverse the weapons.  So the Navy designed a circular, pivoting platform.  To traverse the mortar, crews would raise the platform on four eccentric wheels using braking leavers.  Once raised, the crews used block and tackle to pivot the platform.  After heaving to the proper line, the crew released the eccentric brakes, lowering the platform back onto the base, thus ensuring the wheels would not bear the recoil force when fired. 

Mortar and platform on an unidentified schooner (Wiki Commons)

In addition to the mortars, the schooners carried self-defense batteries.  The larger vessels mounted two 32-pdr guns and two 12-pdr boat howitzers.  The smaller schooners carried only the 12-pdrs. 

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)

The mortars damaged casemates, broke levees, and dismounted some of the Confederate guns.  In Fort Jackson, the garrison huddled in casemates while the fort flooded.  The bombardment continued on for days.  Yet in spite of the impressive display, Porter's mortars did not reduce the forts to rubble as some predicted.  Instead, the Confederate defenders remained active and continued to return fire.  The mortar gunners had difficulty timing their fuses. Some shells burst too high, while others landed on the soft ground and buried too deeply.  Furthermore, Porter complained of the difficulty of spotting and adjusting fires (not unlike that encountered at Island No. 10).  The bombardment was not doing enough damage to suppress the Confederate defenders.

 

Frustrated, Captain (later Admiral) David Farragut decided to run past the forts instead of waiting for Porter's mortars to complete their task.  The mortars continued firing to cover preparations.  After Farragut forced passage on April 24, Porter continued efforts to reduce the forts.  While the mortars failed in terms of physical damage to the forts, their impact took a toll psychologically on the garrisons.  On April 29 many enlisted men in Fort Jackson mutinied and demanded the garrison surrender.  Both Confederate forts capitulated the next day. 

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.