In the early days of Islam there was no standing army. On the occasion of any battle contingents were raised from the various tribes and these were disbanded when the battle was over. No regular salaries were paid. Those who fought were compensated by distributing the spoils of war among them.
Umar was the first Muslim ruler to organise the army as a State Department. This reform was introduced in 637 A.D. A beginning was made with the Quraish and the Ansars and the system was gradually extended to the whole of Arabia. A register of all adults who could be called to war was prepared, and a scale of salaries was fixed.
The scale was:
(l) Those who had fought in the battle of Badr 5,000 dirhams.
(2) Those who had fought in the battle of Uhud 4,000 dirhams.
(3) Those who had migrated before the conquest of Mecca 3,000 dirhams.
(4) Those who had embraced Islam at the time of the conquest of Mecca 2,000 dirhams
(5) Those who had fought in the battles of Yermuk or Qadissiya 2,000 dirhams.
(6) For the Yamanites 400 dirhams
(7) Those who had fought after the battles of Yermuk and Qadissiya 300 dirhams.
(8) The rest 200 dirhams
All men registered were liable to military service. They were divided into two categories, namely:
(l) those who formed the regular standing army; and
(2) those who lived in their homes, but were liable to be called to the colours whenever needed.
For the purpose of army administration, Umar established Military Centres which were called 'Jund'. These Centres were set up at Madina; Kufa; Basra; Mosul; Fustat; Damascus; Jordan; and Palestine. At these centres barracks were built for the residence of troops. Big stables were constructed where four thousand horses fully equiped were kept ready for service at short notice at every Military Centre. All records pertaining to the army were kept at Military Centres. Food stores of the commissariat were kept at these places and therefrom sent to other places.
In addition to Military Centres, cantonments were established in big towns and places of strategic importance.
Under the Army Department, there was a separate Commissariat Department. All the food stores were collected at one place, and from there disbursed on the first ot every month.
Pay and Bhatta were disbursed at different times. The pay was paid in the beginning of the Mohurram. The Bhatta was paid in spring and some extra allowances were paid during the harvesting season.
Every tribal unit had its leader called Arifs. Such units if under Arifs were grouped and each group was under a Commander called Umar-ul-Ashar.
Promotions in the army were made on the strength of the length of service or exceptional merit.
Expeditions were undertaken according to seasons. Expeditions in cold countries were undertaken during the summer, and in hot countries in winter. In spring the troops were generally sent to lands which had a salubrious climate and a good pasturage.
Much thought was given to climate and sanitation in the lay out of cantonments and the construction of barracks. Special provisions were made for roads and streets in cantonments, and Umar issued instructions prescribing the width of roads and streets.
When the army was on the march, it always halted on Fridays. When on march, the day's march was never allowed to be so long as to tire out the troops. The stages were selected with reference to the availability of water and other provisions.
Leave of absence was given to army men at regular intervals. The troops stationed at far off places were given leave once a year and some time twice.
Each army corps was accompanied by an officer of the treasury, an Accountant, a Qazi, and a number of interpretors besides a number of physicians and surgeons.
Umar issued instructions laying stress on the teaching of four things to the soldiers, namely: horse-racing; archery; walking barefoot, and swimming.
On the battlefield the army was divided into sections. These sections were:
(1) Qalb or the centre;
(2) Maqaddamah or the vanguard;
(3) Maimanah or the right wing;
(4) Maisarah or the left wing;
(5) Saqah or the rear;
(6) Rid-extreme rear
Other components were:
(1) Talaiah or patrols to keep watch over the movements of the enemy;
(2) Ra'id or foraging parties,
(3) Rukban or the camel corps;
(4) Farsan or the cavalry;
(5) Rajil or the infantry;
(6) Ramat or the Archers.
According to instructions every soldier was required to keep with him several things of personal need. These included among other things needles, cotton, twine, scissors, and a feeding-bag.
Catapults were used extensively in siege operations. Under Umar another machine employed in siege operations was Dabbabah. It was a wooden tower which moved on wheels and consisted of several storeys. The tower was wheeled up to the foot of the fort under siege, and then the walls were pierced by stone throwers' wall-piercers and archers who manned the Dabbabah.
Under the instructions of Umar, suitable arrange, meets were made for the clearance and construction of roads, and bridges. These operations were usually performed by the conquered people under the supervision of the Muslim army.
A remarkable feature of the army organisation under Umar was that he had complete control over the army at all times as if he were present in person at every field. The control was facilitated because of the sense of awe and majesty that the person of Umar inspired. The espionage and intelligence services in the army were well organised. Reporters were attached to every unit, and they kept the Caliph fully informed about everything pertaining to the army.
Under Umar vast conquests were made in Iraq, Persia, Syria, and Egypt and this speaks for the efficiency of the army and the military organisation.