British infantry brigades of the First World War During the First World War 259 infantry brigade s were raised by the British Army , two by the Royal Navy , and one from the Royal Marines . Of these brigades fifty - three were held in reserve or only used for training , while another nine only served in British India . The pre war regular army only had eighteen infantry brigades , with another forty - three serving with the reserve Territorial Force ( TF ) . Once war was declared , the regular army was expanded first by volunteers and then conscripts for what became known as Kitchener ' s Army . At the same time volunteers for the TF formed second line formations . Three infantry brigades served with a division , mostly the same one throughout the war , but some did serve for short periods with another division . At the start of the war four infantry battalion s , with a small headquarters formed a brigade , but by 1918 , with the number of casualties mounting , the brigade was reduced to three battalions . During the same time the firepower of a brigade was increased by the assignment of more machine gun s , eventually as the war progressed , a brigade had their own machine gun company and a trench mortar battery assigned . Background . At the outbreak of the war in August 1914 , the British regular army was a small professional force . It consisted of 247 , 432 regular troops organised into four Guards , 69 line infantry and 31 cavalry regiment s , along with artillery and other support arms . The regular Army was supported by the Territorial Force , and by reservists . In August 1914 , there were three forms of reserves . The Army Reserve of retired soldiers was 145 , 350 strong . The Special Reserve had another 64 , 000 men and was a form of part - time soldiering , similar to the Territorial Force . The National Reserve had some 215 , 000 men , who were on a register which was maintained by Territorial Force County Associations ; these men had military experience , but no other reserve obligation . The regulars and reserves — at least on paper — totalled a mobilised force of almost 700 , 000 men , although only 150 , 000 men were immediately available to be formed into the British Expeditionary Force . Pre war regular army . After 1907 , the regular British Army , serving at home , was grouped into six division s , each of three brigades numbered 1st – 18th . Following the declaration of war , four infantry battalion s , which had been intended to defend the lines of communication , were brigaded together as the 19th Brigade . Near the end of 1914 , when regular army battalions returned to Europe from serving around the British Empire , they formed the 7th and 8th Division , with the 20th – 25th brigades . As the war progressed three more regular army divisions were formed the 27th , 28th and 29th , with their brigades being numbered from 80th – 88th . Territorial Force . The reserve formations of the Territorial Force comprised fourteen divisions each of three brigades , while another three brigades were independent formations intended for coastal defence . They were unnumbered until August 1915 , and took the name of the region they were affiliated with , or the name of the regiments that supplied their battalions . When the brigades were given numbers they became the 125th – 234th brigades . As a home defence organisation , their men could not be sent overseas against their wishes . After war was declared almost to a man the Territorial Force volunteered to serve overseas , so a second line Territorial Force was recruited , virtually a mirror image of the first line divisions and brigades . For example the Northumbrian Division , had the Northumbrian , York and Durham and the Durham Light Infantry Brigade s . The second line 2nd Northumbrian Division , had the 2nd Northumbrian , 2nd York and Durham and the 2nd Durham Light Infantry Brigades . Volunteers for the second line Territorial Force had the same terms and conditions as the first line , and could not be sent overseas unless they agreed to do so . Kitchener ' s Army . The third part of the British Army was the New Army , also known as Kitchener ' s Army . Recruits for the New Armies were technically part of the regular army , serving for three years or until the end of the war . The first of the New Armies comprised the 9th – 14th divisions , with the 26th – 43rd brigades . The second New Army comprised the 15th – 20th divisions , with the 44th – 61st brigades . The third comprised the 21st – 26th divisions , with the 62nd – 79th brigades . The fourth and fifth were the Pals battalion s of the 30th – 35th divisions , with the 89th – 106th brigades and the 37th – 42nd divisions , with the 110th – 136th brigades . The last New Army was the sixth , comprising the 36th – 41st divisions , with the 107th – 124th brigades . Infantry brigade composition . At the start of the First World War French , Russian and German divisions consisted of two brigades each of which were made up of two regiments . Each regiment had four battalions , which meant that in total there were around 6 , 000 men in the brigade . The British Army was different . Their divisions consisted of three brigades , with each brigade having slightly over 4 , 000 men in four battalions , plus support troops , under the command of a brigadier general . The 1914 British infantry brigade comprised a small headquarters and four infantry battalions , with two heavy machine gun s per battalion . Over the course of the war , the composition of the infantry brigades gradually changed , and there was an increased emphasis upon providing them with their own organic fire support . By 1916 each brigade had a Vickers machine gun company and a mortar battery with eight Stokes Mortar s . The machine gun companies were later withdrawn and combined into a divisional machine gun battalion . By 1918 , the brigade formation had been reduced to three battalions . However each battalion now had thirty - six Lewis machine gun s , making a total of 108 in the brigade . Several brigades that served away from the Western Front and other main theatres of operations , had a different composition . The 228th Brigade , which served with the command of the Greek Crete Division , had a Royal Engineers signal section and a Royal Army Medical Corps field ambulance attached . Other brigades that served in the British Salonika Army , had a Section Ammunition Column attached . Brigades that served in the Mesopotamia Campaign had their own supply and transport columns of the Army Service Corps . One brigade , the 226th Mixed , was unique in the respect that it was the only infantry brigade with its own artillery , having two batteries from the Royal Garrison Artillery assigned . In the trench warfare on the Western Front , an infantry brigade ' s defensive responsibilities depended upon where they were at the time . On 21 March 1918 , the first day of the German Spring Offensive , the 173rd Brigade was responsible for of the front line . In 1918 , the British Army was responsible for of the Western Front . The forty - two brigades , fourteen divisions , of the First Army had to defend . The thirty - six brigades , twelve divisions , of the Second Army . The forty - two brigades , fourteen divisions , of the Third Army . The thirty - six brigades , twelve divisions , of the Fifth Army possibly had the hardest task with of front to defend . Within the brigade a typical deployment was one battalion in the front line , with the other two in reserve , about back . The forward battalion had several section s manning outposts in the front trench with two companies manning strong points behind them . Their third company was in reserve to act as a counter attacking force and the fourth company was resting . Two brigades of a division would be deployed forward with the third brigade in reserve .