Battle of Palo Alto

Background

The war began on the lower Rio Grande before it was formally declared. An American fort stood across the river from Matamoros, and Taylor's army of occupation had set up a supply base at Point Isabel, on the coast about 25 miles away. Mexico proclaimed a 'defensive war' on 23 April 1846 and the United States declared war on 12 May, four days after Palo Alto.

General Mariano Arista reached Matamoros on 24 April with orders to dislodge the Americans. He crossed the river upstream after a long wait for boats, and Captain Seth Thornton's dragoons were ambushed and captured in what became known as the Thornton Affair. Taylor left the fort on 1 May and marched to Point Isabel to secure his supplies. Arista began shelling the fort on 3 May, and his army took up a position on the prairie at Palo Alto that cut the road between fort and depot. Taylor was back at Point Isabel by 5 May.

He could not abandon the fort's garrison, so on 7 May he marched south again with about 2,300 men and a train of some 400 wagons. Arista drew up across the road on open grassland. The two armies sighted each other about noon on 8 May.

The armies

Taylor commanded a small regular army: infantry regiments under Colonel David Twiggs and Lieutenant Colonel William Belknap, dragoons, and artillery. Its strength lay in its guns. Major Samuel Ringgold's light, horse-drawn 'flying artillery' could be moved quickly and fired accurately, and Captain James Duncan's battery was another. Churchill's battery brought two 18-pounder siege guns that had originally been meant for the fort. Taylor was also anxious about his 400 wagons, which tied him to the road and shaped every decision he made that afternoon.

Arista's Army of the North had perhaps 3,200 to 3,700 men: infantry brigades under Generals Rómulo Díaz de la Vega, José María García and Pedro de Ampudia, and a strong cavalry arm under Anastasio Torrejón, which anchored a line roughly a mile long. His artillery was lighter and, on the sources' account, less effective: Mexican 4-, 6- and 8-pounders often fired short.

Wikipedia's order of battle section is itself flagged as unsourced, so the unit-level detail here is limited to what the NPS, the Handbook of Texas and Wikipedia's prose agree on.

The battle

Deployment (about noon to 2 p.m.) Taylor reached the field about noon, paused to organise his wagon train and then advanced to within about 700 yards of Arista's line. The Mexican army faced north, with cannon on the road, infantry and artillery across the field and cavalry on the flank. Taylor halted and formed his line behind his batteries. Fearing that a charge would expose his wagons, he held his infantry and dragoons back and let the guns work.

Opening cannonade (about 2 p.m.) The Mexican guns opened first, and the American artillery answered more effectively. The 18-pounders and Duncan's and Ringgold's light batteries tore gaps in the Mexican line, while Mexican round shot often fell short.

First cavalry attack and the grass fire Arista sent Torrejón's lancers against the American right. Uneven ground and dense growth slowed them, and Twiggs formed the 5th Infantry into square, which turned them back with a few volleys. They tried again for the wagon train and were again repulsed, with the light artillery helping. Then a fire, started in the dry grass by a burning cannon wad, spread across the field. Its smoke and Taylor's concern for his train halted the action for about an hour. Afterwards Arista pulled his left back about 1,000 yards and Taylor advanced, rotating the battle line about 40 degrees counter-clockwise.

Ringgold falls; the second attack (afternoon) Mexican guns replied to the American batteries and mortally wounded Major Ringgold, creator of the light artillery. Arista then attacked the American left. Lieutenant Colonel Charles May tried to turn the Mexican left, and Childs's artillery battalion, serving as infantry, formed square against another charge by Torrejón's horse. Duncan's battery blocked the attempt to turn the American left, and quickly changed position to break up attacks on the wagon train. Wikipedia then has Duncan advancing with the 8th Infantry and Ker's dragoons, and says that when Arista ordered a charge his light cavalry fled along the line and took the 6th Infantry with them; the NPS says a Mexican cavalry counter-attack stopped Duncan's advance.

Dusk After roughly four hours of cannonade, the Handbook of Texas puts a last desperate Mexican charge at sunset. The NPS says the Mexicans, short of ammunition, withdrew to the southern edge of the field about 7 p.m. and Taylor camped behind his own lines. Both armies spent the night on the field, and the Mexicans buried their dead.

This is a single CDB90 engagement ('PALO ALTO', 14:30 to 19:30).

Aftermath

Losses were lopsided. American casualties were between 48 and 58 on the sources' counts, and the Mexican army lost at least 257 men by Arista's own commissary and perhaps 400 by Meade's estimate. The Americans lost Ringgold, mortally wounded.

Arista declined a second day on the same ground. After burying his dead he withdrew at first light on 9 May to Resaca de la Palma, a ravine position where he hoped to neutralise the American guns, and Taylor attacked him there and won decisively. The Americans then took Matamoros and Arista fell back towards Monterrey.

Taylor became a national hero, and the battle is remembered as the vindication of Ringgold's light artillery, whose mobility the sources credit with winning the day. Palo Alto Battlefield National Historical Park, authorised in 1978 and established in 1992, is the only National Park Service unit that interprets the war, and Iowa named counties for the battle and its participants.

Wargaming it

Palo Alto is one of the best small artillery duels in the black-powder era, and it is easy to set up: a flat open prairie, no villages, two lines about 700 yards apart. A single table at battalion or battery scale works, with each gun model standing for a section or battery and each infantry unit for a company or battalion. The terrain is trivial, which is the point: the game is about movement and ranges.

The central asymmetry is mobility versus mass. The American player can shift batteries every turn, but must keep a force back to protect the wagons; the Mexican player has numbers and a cavalry arm that can threaten the wagons and the flanks, but cannot easily hurt a unit in square. Cavalry versus square is the main tactical question, and it should usually go against the cavalry. Mexican guns should be less accurate at range.

Two mid-game events give the scenario shape. The grass fire can be a random event that blocks line of sight for a turn or two, and can be used to rotate the front. Ringgold's wounding can be a scripted morale shock for the American artillery. Victory could turn on whether Taylor keeps the wagons intact and drives Arista off by dusk. The 'what if' is Arista pressing the right flank early, before the light batteries had found their range, or using the smoke from the fire to bring up his infantry.

Maps and pictures