“I have carefully searched the military records of both ancient and modern history, and have never found Grant’s superior as a general,” wrote Robert E. Lee. This statement is, in essence, the argument of John Mosier’s “Grant: A Biography” (Palgrave Macmillan, 224 pages,. $21.95), an outstanding contribution to General Wesley Clark’s Great Generals Series. Indeed, Mr. Mosier’s brief for Grant might be called a thesis biography, one that counters other biographies ranking Grant lower as a general, using criteria Mr. Mosier deems suspect.

Designed as incisive re-evaluations of American military figures, the contributions to General Clark’s series are forced to cover a good deal of ground quickly. Mr. Mosier solves his logistical problem by dispatching Grant’s early life before he attended West Point in less than two short chapters.

Grant was in most respects ordinary, contends Mr. Mosier, who finds fault with biographers who seek signs of greatness in their subject’s formative years. What distinguished the 40-year-old Grant, Mr. Mosier emphasizes, was his aptitude for the job of generaling and his rugged determination to forge ahead no matter the obstacles. Grant shared with Napoleon an affinity for mathematics, an ability to “compute precisely all the quantitative data required to make correct decisions on the battlefield.” This was not a matter of formal education. In fact, Grant taught himself algebra, an indication, Mr. Mosier suggests, of a highly developed “capacity for abstract thought.” Grant’s predecessor, George McClellan, had more distinguished academic credentials, but McClellan consistently overestimated the Confederate army’s strength and lacked Grant’s will to engage the enemy in battle.

Just as important, Grant had a talent for drawing and painting. Both were required skills at West Point at a time when soldiers were not issued contour maps and were expected to make their own. Wherever Grant fought, Mr. Mosier observes, he had in his mind a visual sense of the terrain. Although Mr. Mosier does not make the comparison, again it is Napoleon, a superb map reader, who comes to mind.

Finally, as a third example of what made Grant great, Mr. Mosier mentions his subject’s voracious reading of history and fiction. Grant favored novels that gave him insight into human nature and helped him – like Admiral Nelson, I would suggest – identify closely with the men he sent into conflict. At a time when most armies were filled with the dregs of society driven by an arrogant officer class, Grant treated his citizen-soldiers with respect.

But there is more to Grant’s reading of literature and history that sets him apart from, say, Henry Halleck, Grant’s commanding officer for much of the early part of the Civil War. The bumptious Halleck considered himself a military theorist and openly scoffed at what he thought of as the overly aggressive Grant’s ignorance of the latest premises of modern warfare. Grant stupidly went right at his enemy, taking huge casualties, rather than concentrating on gaining ground and occupying population centers. The trouble with Halleck’s approach – as with McClellan’s – was that the South concluded that the Yankees did not want to fight, a belief that reinforced Lee’s reputation for invincibility, heartened the Confederacy, and demoralized Northern armies and public opinion.

Grant proceeded not by theory but by examining the conditions in which he had to fight, the concrete particulars of history, not abstract models of how war should be fought. Just as crucial was his ability to translate his vision to his fellow officers. Grant’s lucid and engaging memoirs have brought him acclaim, and Mr. Mosier suggests that that same clarity is evident in Grant’s orders to trusted colleagues such as Sherman on his way to the siege of Vicksburg:

You will proceed, with as little delay as possible, to Memphis, Tennessee, taking with you one division of your present command. On your arrival at Memphis, you will assume command of all troops there. … As soon as possible, move with them down the river to the vicinity of Vicksburg, and with the co operation of the gunboat fleet under the command of Flag-officer Porter proceed to the reduction of that place in such manner as circumstances, and your own judgment, may dictate.

“Your own judgment” – a key phrase in Grant’s lexicon. Once, when he was not as certain of an officer as he was of Sherman, Grant actually accompanied an attacking force a few miles to steel his subordinate’s will.

Mr. Mosier has little patience with Grant’s critics. Speculation about the general’s drunkenness, press criticism that he recklessly risked lives in battle, and just about every other fault attributed to Grant are dismissed. If Grant ever failed, it was because he relied on certain of his associates too much. Such misplaced trust is what got him into trouble as president, Mr. Mosier suggests.

Unlike Napoleon or Wellington, Grant had to superintend far-flung battlefields; his illustrious predecessors remained with a single attacking force. Grant often fought on the kind of difficult terrain (think of his titanic struggle with Lee in the Battle of the Wilderness) that European armies avoided. Grant is greater, in Mr. Mosier’s book, because he surmounted more difficult obstacles than his competitors took on.

Mr. Mosier writes with great conviction and concision. It is easy to fall under his spell. His case for Grant is bracing because he brings to it a world perspective – for example, comparing Grant’s maneuvers to the early German successes in World War II (the Germans studied Grant’s battles carefully) and to Field Marshall Montgomery’s campaigns. If Grant is their superior, it is because he saw both the big picture (strategy) and how to implement it (tactics). Rarely are generals able to function on both macrocosmic and microcosmic scales.

But while I find Mr. Mosier persuasive, I wonder about his methodology. I looked up the Lee quotation in Mr. Mosier’s notes, which read “as quoted by John G. Wilson, ‘General Grant’ (New York: Appleton, 1913), p. 367.” Where and when did Lee make his tribute to Grant? It is such a powerful statement that I was surprised Mr. Mosier did not use it as an epigraph to his entire book. Obviously, Mr. Mosier believes Wilson is a good source, but I want to know more – if there is more to know.

In “General Ulysses S. Grant: The Soldier and the Man” (Perseus, 338 pages, $26), the military historian and biographer Edward G. Longacre challenges many early sources on Grant’s life and career. Wilson’s book appears in Mr. Longacre’s bibliography, but what he would make of Lee’s praise I do not know – although from his painstaking re-enactment of Grant’s battles it seems certain that Mr. Longacre would not rank Grant as highly as Mr. Mosier does.

Here is Mr. Longacre comparing Grant’s siege of Vicksburg to his earlier battle at Shiloh: “Fortunately, the man who would oversee this work was not the cautious, tentative commander Grant had become at Shiloh. The bold, assertive, risk-taking side of his personality had reasserted itself – just in time to elevate his career to the next level.” Earlier in his narrative, Mr. Longacre quotes extensive press criticism of Grant’s command at Shiloh and even credits the reports that the general had been drunk during part of the engagement with the enemy.

Historians have challenged virtually all evidence of Grant’s drunkenness. Some of it, Mr. Longacre concedes, is unreliable, the product of envious rivalries and irresponsible reporting. But not all of it can be dismissed so quickly, Mr. Longacre suggests. He calls Grant an alcoholic, whereas Mr. Mosier – while conceding that on occasion Grant drank too much in the 1830s and perhaps again in the 1850s – concludes “he seems to have overcome the problem long before the Civil War began.”

Nowhere does Mr. Mosier detect alcohol abuse undermining Grant’s effectiveness as a military man, which is perhaps why he so readily discounts reports of his subject’s drunkenness. And regarding Shiloh, Mr. Mosier does not even see the same engagement Mr. Longacre presents, remarking on Grant’s “unshakable determination.” Moreover, Mr. Mosier calls into questions the very manner in which historians have presented accounts of Shiloh:

The result is a curious sort of history. Shiloh was a Confederate defeat because of Beauregard’s incompetence or timidity; it was nearly a Confederate victory because of Grant’s carelessness. In this regard, Shiloh sets the pattern for much that has been written about the war, which thus takes shape as an account of failures and contingencies, as a demonstration of bumbling, in which hundreds of thousands of Americans were slaughtered owing to fundamental errors made by the generals.

In reality – or as close to it as we are likely to get – Shiloh was a desperate struggle because it matched a military genius with an experienced and able general of the first rank, because their subordinates were first-class officers, and because the soldiers on both sides fought with exemplary courage.

What makes Mr. Mosier such an attractive writer is his iconoclasm and his ability to reargue history and biography. For example, on the question of whether Grant was a mediocre student at West Point, the biographer points out that it depends on how you interpret the numbers. While Grant graduated 21st in a class of 39, there were 70 entering cadets, which meant that half dropped out. Was Grant then at the bottom of the class or in the top quarter? Mr. Mosier asks.

Mr. Mosier would certainly scoff at the sources of some of Mr. Longacre’s evidence, such as the one in which a bystander, noticing that the 2-year-old Grant does not flinch when his father fires a gun, exclaims, “that boy will make a general!”

Because Mr. Longacre is mired in too much detail and is too little concerned with Grant’s overall strategy, I prefer Mr. Mosier’s polemical biography, written with such verve and directness that it is rather like the subject he so admires.