Certainly the oldest military title that survives in most modern armies is that of captain, from the Latin caput, “head,” and thus the head man. It is notable that in the German army the word for captain is hauptmann, which means precisely “head man.” Almost all modern military titles are drawn from the period when feudalism was dying and when the power of central governments was crystallizing, forming in the process royal or regular armies for the service of the state.
At that time, the title of captain was usually given to the commander of a company, which was the largest and about the only recognized subdivision of these new armies and usually numbered 300 or 400 men, or about as many as could be controlled by one leader on the battlefields of that time. The title itself, however, was of feudal origin. In feudal times, it had been customary for each lord to retain a certain number of armed men to guard his castle; these gradually came to be commanded by a captain, who was not usually a knight or of noble blood but a hired mercenary, trained and experienced in war, who, in most cases, had fought his way up from the ranks. His men, the only trained soldiers of the feudal period, were used to drill the raw levies that were mustered whenever the lord’s suzerain called on him to take the field with his allotted quota of men for war. The complete quota was almost never kept under arms in time of peace. The trained soldiers were known as the lord’s servants, or serventes, which, in military parlance, became corrupted into sergentes, or sergeants. Thus, a feudal levy had not only a group of knights and squires at its head but a captain and several sergeants over a body of more or less raw recruits. The richer the lord, the larger the proportion of trained men at his disposal.
When the royal armies began to appear, the captain became a much more important person. He commanded a company of royal troops instead of the scratch castle guard of a baron or an earl. The jobs were better paid, and consequently were sought after by young men seeking both money and a chance for distinction. Sergeants were also a part of these troops and did much the same work that sergeants have done ever since. As the centralization of power in the king’s person grew, the new and noble captains found that their personal interests required them to spend more time at court and less in the field, and to accomplish this, they hired officers to take their place in the actual command of their companies. These were called placeholders, or, in the term derived from the French, lieutenants.
As the armies grew in size, the number of companies became greater and it was usual to find several companies marching together in column on the same road. The senior officer present commanded the whole column, called colonne in French, and from this source he came to be known as the colonel, or column commander. Later, these columns became permanent regiments, and the same thing happened as with companies; the colonels, to retain their lucrative jobs, frequented the court and secured the services of lieutenant colonels to command their regiments on active service.
Finally, the command of the whole army was given to an officer who originally was called the general captain, or captain general, in distinction to the company captain, who commanded just one company. He, too, had to have a lieutenant general to command for him, or at any rate to assist him, and to this end, the “captain” part of this title was dropped, and officers included generals and lieutenant generals, as well as colonels and lieutenant colonels and captains and lieutenants. At the lowest command level were the usual sergeants. This is the framework of the modern military order, although there have been some later additions, notably the ranks of major general and major.
In the time of Oliver Cromwell, the “new model” army was organized with just about the ranks noted above. In each regiment, however, the need was found for an administrative and supply officer to look after the accounts and the paper work, which Cromwell insisted be carefully kept. Cromwell was doubtless influenced by the example of the Swedish king, Gustavus Adolphus (1594-1632 [C.E.]), in whose army many English officers had served out of sympathy for the Protestant cause. Gustavus Adolphus provided his army with a complete administrative organization, which Cromwell adapted to English requirements. In each company a sergeant was appointed to perform the duties of both administration and supply, but at the regimental level an officer was so detailed, and was called the great sergeant, or sergeant major. He took rank next after the lieutenant colonel, being senior to all the captains. Then a corresponding appointment was made for the whole army, as the sergeant-major-general, but the “sergeant” part of both titles was dropped later because the officers concerned doubtless considered it somewhat belittling, and the designations became major and major general. These titles have persisted in the British and American armies to this day. This series of transitions explains, incidentally, why the modern major general ranks one grade below a lieutenant general, while a major is two grades higher than a lieutenant. The grade of sergeant major, in its actual meaning, was later revived for a senior sergeant, a noncommissioned officer.
The title of field marshal, as applied in the British and German armies, or marshal, in the French and [Russian] armies, comes from the old French mareschal, which originally meant a blacksmith or tarrier. In the French army a farrier still has the title of maréchal ferrant. As time went on, the king’s horseshoer, or farrier, rose in importance until the title became equivalent to “master of the horse” at the French court and gradually assumed great military importance. Later, in the French royal armies of the 18th century [C.E.], the need was felt for a rank of subordinate general officers, as in Cromwell’s army, to take charge of the camp, administration, the divisions of the army, and so forth. By that time, the original importance of the title had been lost, but it was revived as maréchal de camp, which was about the equivalent of the major general of the British Army in status, ranking below the lieutenant general but senior to all colonels. This title disappeared under Napoleon, who, however, created the higher title of marshal of the empire, for a senior general officer ranking all generals and serving generally as the commander of an army or an army corps. In the British Army, the title of field marshal as the highest ranking grade was first known in 1736.
The origin of the title of corporal is somewhat obscure. The word seems to have an Italian source, corporale, from the Latin corpo, meaning body, and hence the person in charge of a small body of troops. It appeared in Cromwell’s time in the British cavalry, who, feeling superior to the infantry, wanted a title of their own for noncommissioned officers; they called them corporals instead of sergeants, and, in the British household cavalry regiments, the sergeants are still officially called corporals of horse. Later the title was used to fill the need for an inferior grade of noncommissioned officer….
The ranks of first and second lieutenant developed as companies grew in size and weapons in range and power, so that a company needed three officers instead of two for proper control. Originally, the third officer of an infantry company was called ensign, because part of his duty was to carry the company flag; for the same reason the third officer of a troop of cavalry was the cornet, because he carried a little pennon known then by that name. Later, the flags were laid aside, and these junior officers became known as second lieutenants.
The British titles of lance corporal and lance sergeant, which mean “acting corporal” and “acting sergeant,” were derived from the old lance-pesade, a term used during the 17th century [C.E.] for a full-trained soldier of a grade superior to the common men, or private men, as they came to be called.
— [undocumented encyclopedia entry]
Emphasis mine.
