They served on horseback patrolling the water ways. Very similiar to what our Coast Guard was doing along the Atlantic seabord during the early days of WWII.

Payton Bland, age 49, 1st Lieutenant, Company I, 13, Regiment Texas Cavalry,* enlisted March 1, 1862 at Orange, Texas by S. A. Fairchild for 12 months, resigned and discharged by Conscript May 24, 1862

* This company was known at various times as Captain Fairchild's Company, Company K and Company I, 13th Regiment Texas Cavalry

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Peyton, Bland, Captain Merriman's Company, (Orange County Coast Guards) Texas Local Defense Troops, his name appears on a June 9, 1862 muster roll at Orange, Orange County, Texas, no other records

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Peyton Bland, Captain, Company E, 1st Regiment Texas Cavalry, State Troops, present Post at Sabine Pass, Texas November, 1863, stationed at High Island December, 1863, no other records

M323: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Texas

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BLAND, PAYTON, 1ST LIEUTENANT, Enlisted in the service of the Confederate States of America and served Honorably in the Orange County Coast Guard, Merrimans Company, Local Defense Troops, C.S.A. Mounted Confederate Soldiers that patrolled Orange County, Texas water ways on horseback for enemy activities and ships. Also served in Company I, 13th Texas Cavalry, Flowernaughts, later Dismounted. (note: Company I was formed in Orange County, Texas.)
http://archiver.rootsweb.ancestry.com/th/read/TXORANGE/2000-06/0961545017