Tambo (fondly known as O. R.) was born on 27 October 1917 in the village of Nkantolo in Bizana in eastern Pondoland in what is now the Eastern Cape. His father, Mzimeni Tambo, was the son of a farmer and an assistant salesperson at a local trading store. Mzimeni had four wives and ten children, all of whom were illiterate. His mother, Mzimeni's third wife, was called Julia.

During his early years with the ANC, Oliver Tambo was directly responsible for organizing active guerilla units. Along with his comrades Nelson Mandela, Joe Slovo, and Walter Sisulu, Tambo directed and facilitated several attacks against the apartheid state. One of the most notable of these attacks was the Church Street bombing on 20 May 1983, which resulted in the death of 19 civilians and the wounding of a further 217. In submissions to the TRC in 1997 and 1998, the ANC revealed that the attack was orchestrated by a special operations unit of the ANC's Umkhonto we Sizwe (MK), commanded by Aboobaker Ismail. Such units had been authorized by Oliver Tambo, the ANC President, in 1979. At the time of the attack, they reported to Joe Slovo as chief of staff, and the Church Street attack was authorized by Tambo.  The ANC's submission said that the bombing was in response to a South African cross-border raid into Lesotho in December 1982 which killed 42 ANC supporters and civilians, and the assassination of Ruth First, an ANC activist and wife of Joe Slovo, in Maputo, Mozambique. It claimed that 11 of the casualties were SAAF personnel and hence a military target. The legal representative of some of the victims argued that as they were administrative staff, including telephonists and typists, they could not be considered a legitimate military target.  Ten MK operatives, including Aboobaker Ismail, applied for amnesty for this and other bombings. The applications were opposed on various grounds, including that it was a terrorist attack disproportionate to the political motive. The TRC found that the number of civilians versus military personnel killed was unclear. South African Police statistics indicated that seven members of the SAAF were killed. The commission found that at least 84 of the injured were SAAF members or employees. Amnesty was granted by the TRC

Using a quote from the above article, answer the following question: What was the most risky activity Tambo did?
Tambo directed and facilitated several attacks against the apartheid state.