Six men, armed with knives and noxious gas, followed nine couriers across Westminster before assaulting them on the street, on buses and in tube stations.
The robberies took place at Kings Cross Station, Knightsbridge Underground Station, on buses near Hyde Park Corner and Park Lane and on streets across Westminster between July and November 2014.
Detective Sergeant Tony Skinner, of the Met Police's Flying Squad, said: "The victims were moving large amounts of cash for bureau de change shops. The gangs watched them leave the premises, and then followed them before launching their assaults."
"They are an incredibly violent gang who thought nothing of attacking their victims in crowded places. On a number of occasions, they stabbed their victims and sprayed a noxious substance into their eyes. They even turned a knife on a member of public who chased them."
The gang robbed seven of their victims of a total of £120,000 but failed to get any money from another two.
The Flying Squad began investigating after identifying a trend in the attacks. On 25 November 2014, they arrested three men after observing them follow a man to Bayswater. The victim went inside a building and the gang got on a bus to Victoria in the hope, detectives believe, of locating a new victim. Detectives arrested the men as they got off the bus.
