They have also arrested a 55-year-old man as law enforcement agencies in the United States were conducting a possible link to an operation in New Jersey.
Officers with search warrants raided two residential and one business address in and around Dartford at 6am.
At one of the houses police found hundreds of firearms, including shotguns and automatic and semi-automatic weapons.
The arrested man was held on suspicion of supplying firearms.
Scotland Yard said the searches were the culmination of a major operation - codenamed Mokpo - to tackle the supply of guns to criminals in London.
The raids had been planned for 18 months and were conducted by officers from Scotland Yard's Operation Trident, which targets gun crime and drug-related killings in London's black community.
"This operation has resulted in hundreds of guns being taken out of circulation and has potentially prevented a number of serious injuries or even deaths occurring on the streets of London," said Detective Chief Superintendent Kevin Davis.