Mexican war.Graduating in 1842, he was still a second lieutenant when he was ordered with his command into active service in Mexico in August, 1845. During the three succeeding years he participated in nearly every battle fought by our forces under the command of either Scott or Taylor, and always attracted the notice of his superior officers by his conspicuous courage. He soon rose to the rank of first lieutenant, and for gallant conduct at Contreras and Cherubusco, was breveted captain. At Chapultepec he volunteered with the storming party, and so distinguished himself among the scores of brave men who participated with him in that desperate assault as to win for himself a second brevet as major. He was one of the six officers in the whole force employed in Mexico who were twice breveted for meritorious service upon the field. Animosity, envy and a disposition to indulge in carping criticism have led to many unjust reflections upon General Hill, but the most unscrupulous of his detractors never questioned his courage or his integrity. When the legislature of his native State provided by law that three swords should be awarded to the three bravest of her soldiers who had survived the war with Mexico, many letters and testimonials from the officers of the old army were voluntarily sent to the Chief Executive, naming D. H. Hill as among the bravest soldiers in the army of the United States. Among the few of these testimonials still extant is the letter from the gallant Bee, who, in exclaiming a moment before he fell at Manassas, ‘There stands Jackson like a stonewall,’ gave to the great leader the pet name by which his soldiers called him and the world knows him, and thereby made himself immortal as its author. The letter, addressed to General Dunavant on the 26th of October, 1856, is as follows:
It gives me great pleasure to add my mite of praise to that which has already been given to Mr. Hill by his military superiors. I had the pleasure of knowing him intimately and serving with him in the storming party detailed from Twigg's division for the attack on Chepultepec. I can bear full testimony to his gallantry and to his ardent desire to do his duty well. In addition, I can testify to his State  pride, evinced in his going up under a heavy fire to congratulate and praise a member of the Palmetto regiment, who was behaving under fire most gallantly. For his services on that day he received honorable mention from his immediate commanders and also from Colonel McGruder, commanding a light battery, which battery Lieutenant Hill offered to support when it was menaced by a body of Mexican lancers. He received the brevet appointment of major, and was considered a loss to the service when he resigned. Your obedient servant,
Bernard Bee, Captain U. S. Army.
From the scores of her surviving heroes of the Palmetto regiment and in the regular army the committee appointed by the State authorities selected Hill to receive one of the three swords awarded, and it is still preserved by his family. After the close of the late war a Federal soldier wrote to General Joseph E. Johnston asking the name of a Confederate officer who, on the right of our army at Seven Pines, had made himself most conspicuous for his daring and indifference to danger. The only mark of distinction which he could give General Johnston was that he thought the officer rode a white horse. General Johnston replied that he supposed the officer referred to must have been General D. H. Hill. In writing to General Hill about the matter, General Johnston said: ‘I drew my conclusion that your horse might very well have been taken for white, and that no man was more likely to expose himself than you. Do you know that in Mexico the young officers called you the bravest man in the army?’