These notes are taken from Maurice's History of the War in South Africa, Vol 4.
At the beginning of the campaign the strength of this corps was three officers, eighty-nine other ranks, composing one company of the 24th Middlesex (Post Office) Volunteers. These men, like all the 24th Middlesex, were drawn from the London Post Offices, and were those who had been specially enlisted for a period of six years in the Army Reserve to render them available for foreign service. This original force, which proceeded to the seat of war in October, 1899, soon became totally inadequate to the growing needs of the Army. Reinforcing drafts followed rapidly, drawn at first from the 24th Middlesex, but later from the postal services of all the provinces of Great Britain, and even to a small extent from those of Canada, Australia, Cape Colony and India. The greatest strength attained at the height of the campaign was ten officers, a warrant officer, and 396 other ranks, with, in addition, twenty civilian clerks and 100 soldiers attached for orderly duties.
The system was founded upon a Base Office at Cape Town (a base office for Natal at Pietermaritzburg was employed in the earlier part of the campaign, but discontinued later). From this radiated a number of forwarding offices, which served for intermediate despatch of mail matter, and for the reception and forwarding of cross-post letters. Next, the fixed camp and station post offices, seventy-one in number, dealt directly with the receipt and delivery of mads to tne troops at and around normal centres of operation. Finally, there was a system of travelling post offices, which, traversing the railways in box trucks and sorting carriages specially fitted up by the Imperial Military Railways, delivered and received mail matter, cashed and sold postal orders at any spot upon the lines where their services were required. The bulk of the work which fell to the Army Post Office Corps was naturally that of the distribution of the inward mails and the exporting of the mails for oversea. The former presented extra- ordinary difficulties. The railway service, being completely beyond the control of the Post Office Department, could not be relied on for automatic delivery of the mails. Trains were apt to be delayed for military purposes, or by the enemy who frequently destroyed them. In the latter case the Post Office men on the train would be called upon to take rifle in hand and defend their charge. Thus at Roodewaal, June 7th, 1900, an officer and nineteen men of the A.P.O.C. fought with the troops, and lost five killed and wounded, and fifteen taken prisoners. On that occasion 2,000 bags of mails were destroyed by the enemy, and postal stock (stamps, postal orders, etc.) lost to the value of £4,284. On two other occasions travelling post offices were captured by the enemy. Another complication was that units and individuals were in incessant movement and flux. Forces were broken up or transported rapidly from one end of the theatre of war to the other, or were perhaps unapproachable, or even not to be traced at the required moment. Individual officers and men constantly, and several times in a short period, left their units for duty in other parts, for hospital, for leave of absence, or for home. Their letters and parcels were frequently insufficiently addressed. " Private Smith, Field Force, S. Africa," was an actual conundrum which regularly confronted the Post Office officials. Many correspondents, too, instead of quoting the corps of the intended receiver of their missive, would merely inscribe his last address, possibly that of a place at which he had only halted for a few hours or minutes. Finally, very many men—e.g., the batches of Imperial Yeomanry—arrived in South Africa without regimental numbers, posted to no unit, and generally almost unidentifiable as soon as they had disappeared into the enormous whirlpool of the campaign. In short, there was no difficulty with regard to the actual identification of packages which did not present itself in full measure at every arrival of a mail.
With all these, and many other formidable difficulties the APOC coped with, in general, extraordinary ingenuity and success The greatest obstacle in the early part of the campaign, that of getting timely information of the multitudinous movements of detached units and men, was surmounted by the institution of a system of rolls, which were sent weekly from all hospitals, depots, departmental corps, casualty offices, etc., into the Base Office at Cape Town. Alphabetical lists of names were carefully compiled from these. So elaborate became the system of listing, that the APOC was often able to furnish other military departments with the whereabouts of an individual who had got out of ken. The mode adopted of distributing an incoming mail was briefly as follows: Since mobile units instead of fixed stations had to be dealt with, the sorting, instead of being divided into "roads," and divided according to military units. It was next sub-sorted into twenty-four alphabetical divisions, which on comparison with the above-mentioned alphabetical lists, furnished at once information regarding any detached addressee. The "redirections" were divided into two classes : (i.) "ordinary," i.e., individuals who were constantly absent from their proper units on detached duty ; (ii) "casual," such as patients in hospital, persons on leave of absence etc. An APOC officer was allocated a certain batch of units as his peculiar charge, and these he catered for, irrespective of their geographical position at the moment. To economise time, labour and expense in telegraphing, etc., each unit was given a code number, which it bore throughout the campaign in all the offices of the APOC. Latterly, when the troops became almost exclusively embodied in mobile columns, columns superseded corps as Post Office units. The mails for the several columns were then made up separately, so that even if consigned to an abandoned address, they could be redirected en bloc, diverted to any point, and, if necessary, follow the columns about until caught up. The following figures relative to the extent of the dealings of the APOC may prove of interest :—
(i) Greatest number of Army Post Offices at work, 71.
(ii) Average number of articles received each week at Cape Town: Letters, 190,000, Newspapers and packets, 300,000, Parcels, 8,400
(iii) Heaviest mail received (December 24th 1901): Letters 303,000, Newspapers 368,000, Parcels 31,858
(iv) Value of Postal Orders sold in the field: More than £ 1,000,000
(v) Casualties of APOC: Killed, 2; wounded, 3; died of disease, 45.
(vi) Average weekly account rendered to the Comptroller and Accountant-General, London £400,000