Despite its poor reputation, the SRB occasionally succeeded in uncovering plots aimed at deposing Amin. In 1977, it discovered that Ugandan exiles in Kenya were planning to invade Uganda. The SRB consequently forewarned the President, and the Uganda Army successfully repelled the invasion. By 1979 the bureau employed about 3,000 men and women as agents, many of them Nubians. Most of them fled Kampala when the city fell to Tanzanian and Ugandan rebel forces in April 1979. Shortly before they left, several agents tossed grenades into the holding cells of the SRB headquarters, killing about 100 detainees. The Tanzanians freed 13 survivors.