[3] As training progressed, they heard rumors, which proved true, that the regiment was bound for duty with Major General (MGEN) Benjamin Butler in the Gulf of Mexico.

[18] The expeditionary force and its small fleet of steamer transports and towed sailing supply vessels arrived at the mouth of the Rio Grande shortly after noon, November 1, 1863.

General Cobos received permission from the civilian authorities in Brownsville to organize a force to resist the looters and subdue the fires started by the Confederate evacuation.

The forces under MGEN Washburn remained at Aransas Pass for five days[33] preparing their continued advance north along the Texas coast toward Matagorda Island.

The 100 picked men were from companies C, H, and K.[39] The patrol embarked on USS Granite City and traveled north to a point seven miles (11 km) from the head of the peninsula with an eye to coming upon any rebel scouting force from the rear as they swept south on the island.

Hesseltine spread his men in skirmish order across the width of the island and started sweeping south with Granite City offshore to provide any naval gunfire support (NGFS).

Hearing a whistle from Granite City and then the firing of its 30-pounder (14 kg) gun, he looked at the ship's target with his telescope and saw a large body of Confederate cavalry coming down from the north in his rear.

When it lifted midday, the gunboat CSS John F. Carr steamed down the interior bay to shell the makeshift fort "with her 20-pounder Parrott, making some very good shots, but injuring no one.

In his report Hesseltine sang the praises of all his subordinates the steadiness and tactical proficiency of the men in his patrol, and specifically lauded the two US Navy ships concluding his report with: Captain [George H.] Perkins, of the Sciota, excited my admiration by the daring manner in which he exposed his ship through the night in the surf till it broke all about him, that he might, close to us, lend the moral force of his 11-inch guns and howitzers, and by his gallantry in bringing us off during the gale.

(Some historians have claimed that the campaign was also motivated by the continuing distraction down near the scene of 13th's exploits in the last quarter of 1863, the 25,000 French troops in Mexico sent by Napoleon III and under the command of Emperor Maximilian).

Banks would command this combined force of 30,000, which would be supported in its march up the Red River towards Shreveport by Union Navy Rear Admiral David Dixon Porter's fleet of gunboats.

[49] At this time opposed by a numerically inferior force led by Major General Richard Taylor, Banks and his staff expected no real resistance.

[58]Further, in his post-action report, Banks wrote: Their attack was made with great desperation, apparently with the idea that the dispersion of our forces at this point would end the campaign, and with the aid of the steadily falling river leave the fleet of transports and gun-boats in their hands or compel their destruction.

Upon arrival at Pleasant Hill, Banks had his force prepare for battle and deploy to face the enemy with the 13th in Emory's division in the center left of the line.

[63] At 1630, Confederate BGEN Thomas J. Churchill's arriving infantry started the attack on the Union forces striking Col Lewis Benedict's 3rd Brigade of Emory's Division.

[64][65] The push drove Churchill's infantry back and members of, and, joined by neighboring regiments, they routed Taylor's men from the vicinity of Pleasant Hill.

Unknown to him, the state of his opponent was such that as Kirby Smith wrote, "Our repulse at Pleasant Hill was so complete and our command was so disorganized that had Banks followed up his success vigorously, he would have met but feeble opposition to his advance on Shreveport.

"[67] Short of water and feed for the horses, not knowing where his supply boats were, unaware of the depth of the wound he had dealt his opponent, and receiving divided opinions from his senior officers, Banks opted for a rapid retreat downriver to Natchitoches and Grand Ecore to rendezvous with the fleet.

[70] At Grand Ecore near Natchitoches, Banks received confidential orders from Grant to move the army to New Orleans to avoid further jeopardizing the timetable for the attack on Mobile Bay.

[75] He was determined to seize as much contraband as he could before retreating to the Mississippi and put his regiments on relief from manning the defenses to work loading cotton and sugar on the flotillas transports.

En route to the Mississippi, an running twelve-mile (19 km) engagement of a series of successful Union flanking movements was fought on the road to Mansura on May 16.

In the halt at Masura, the 13th and its brigade discovered a shed with a large supply of tobacco and twenty barrels of salt meat intended for the rebel forces.

Despite other military departments were considered secondary to the Army of the Potomac; and that XIX Corps were under orders to proceed to Fortress Monroe as rapidly as possible, the 13th and its brethren waited for steamers to become available.

Unlike their trip south in 1862, their journey to Hampton Roads was uneventful, "even stormy Cape Hatteras suffered us to pass without a ripple upon the water.

[80][81] For the next week and a half, the 13th as part of XIX Corps chased Jubal Early's raiding force back and forth and up and down the Potomac in defense of the capital until July 24.

[82][83][84] In the ten days since landing at Washington, the regiment bad marched over one hundred and fifty miles, had forded the Potomac once and the Shenandoah twice, and had twice crossed the Blue Ridge.

When, news arrived of McCausland's raid into Pennsylvania and his revenge burning of Chambersburg, they marched back toward Washington reaching Frederick, Maryland, on the afternoon July 31.

[86] On August 3, while at Monocacy, Emory, commander of XIX Corps, informed the Department that the 13th and 15th Maine had yet to receive their veteran furlough earned several months earlier.

The supply depot and the residents' political leanings made it a target for Confederate guerilla activity, but the 13th and the 15th Maine maintained a constant picket around the town and saw off all raiders without loss.

Despite several brief forays including a week at New Creek, Maryland, the 13th remained in Martinsburg until December 27 when orders arrived for all original members of the regiment who had not reenlisted to depart for Augusta to muster out.