As part of the planning a force had been placed at Pitsani, on the border of the Transvaal, by the order of Rhodes so as to be able to quickly offer support to the Uitlanders when they rose. The force was placed under the control of Leander Starr Jameson, the Administrator General for Matabeleland (Mashonaland). The force was around 600 men, mainly from the Matabeleland Mounted Police.
Jameson was frustrated by the delays and decided to act on his own. Jameson sent a telegram to Rhodes warning him of his intentions. On December 29, 1895 Jameson's force crossed into the Transvaal and headed for Johannesburg, numbering a little under 600 men with only a few heavy weapons. The British representatives were horrified at Jameson's actions and publicly disowned the action and called on all British colonists not to offer any aid to the raiders.
Jameson's force first encountered resistance very early on January 1 when there was a very brief exchange of fire with a Boer outpost. Around noon of that day the Jameson force was around twenty miles further on, at Krugersdorp, where a small force of Boer soldiers had blocked the road to Johannesburg and dug in. Jameson's force spent some hours exchanging fire with the Boer, losing several men and many horses in the skirmish. Towards evening the Jameson force withdrew and turned south-east attempting to flank the Boer force. The Boers tracked the move overnight and on January 2 as the light improved Jameson had reached Doornkop where a substantial Boer force with some artillery was waiting. The tired Jameson raiders exchanged fire with the Boer, losing around thirty men before Jameson realized the position was hopeless and surrendered to Commander Piet Cronjé. The raiders were taken to Pretoria and jail.
The Boer government later handed the men over to the British for trial, Jameson was returned to London and was sentenced to fifteen months, which he served in Holloway. The Boer government was paid almost £1 million in compensation by the British South Africa Company.
The affair brought Anglo-Boer relations to a dangerous low and the ill feeling was further heated by the Kruger telegram. From the German Emperor, it congratulated Paul Kruger on defeating the raid, but it also appeared to recognise the Boer republic and offer support - a idea that alarmed and angered the British.