In 1940, volunteers were called for from serving British Army soldiers within certain formations still in Britain and men of the disbanding Divisional Independent Companies originally raised from Territorial Army divisions and who had seen service in the Norwegian Campaign. In November 1940 these army units were organised into a Special Service Brigade under Brigadier J. C. Haydon with five Special Service battalions. By the autumn of 1940 more than 2,000 men had volunteered for commando training, and the Special Service Brigade now consisted of 12 units which were now called commandos. Each commando would number around 450 men, commanded by a lieutenant colonel. They were divided into troops of 75 men and further divided into 15-man sections. The Commandos were all volunteers, seconded from other British Army regiments, but they retained their own regimental cap badges and remained on their regimental roll for pay.
Formation
The Special Service Brigade consisted of five Special Service battalions, numbered one to five. These Special Service battalions were eventually re-designated commandos. The No. 1 Special Service Battalion became No. 1 and No. 2 Commandos. The No. 2 Special Service Battalion became No. 9 Commando. The No. 3 Special Service Battalion became No. 4 Commando. The No. 4 Special Service Battalion became No. 3 Commando. The No. 5 Special Service Battalion became No. 5 and No. 6 Commandos.
Commando brigades
In 1943 the commandos started to move away from smaller raiding operations. They had been formed into brigades of assault infantry to spearhead future Allied landing operations. Of the remaining 20 Commandos, 17 were used in the formation of the four Special Service brigades. The three remaining units No. 12, No. 14 and No. 62 Commandos were left to carry out smaller-scale raids. But by the end of the year these three commandos had all been disbanded, to supply replacements for the other commando units. The formation of the brigades was:
1st Special Service Brigade with No. 3, No. 4, No. 6 and No.45 Commandos.
2nd Special Service Brigade with No. 2, No. 9, No. 40 and No. 43 Commandos.
3rd Special Service Brigade with No. 1, No. 5, No. 42 and No. 44 Commandos.
4th Special Service Brigade with No. 10, No. 41, No. 46, No. 47 and No. 48 Commandos.