Twelve people were arrested in north London after a two-year investigation by Metropolitan Police officers into the sale of illegal firearms, ammunition and controlled drugs.
Three people in Edmonton were arrested on suspicion of being part of an organised criminal network responsible for a non-fatal shooting.
Police also raided seven addresses in Brent and Hertfordshire as part of an ongoing investigation into gang members suspected of committing aggravated burglaries.
In south London, detectives executed four warrants, resulting in the arrests of three men for offences including possession of a firearm with intend to endanger life and conspiracy to supply class A drugs.
Further warrants and arrest enquiries will continue across the capital in the coming days.
Detective Superintendent Nick Blackburn said: “It was a busy morning for Met officers in all corners of London who were up since the very early hours making arrest enquiries and executing warrants as part of our ongoing work to reduce violent crime.
“As part of this week tackling firearms offences, six suspected firearms and numerous knives have already been seized and in excess of 20 arrests made.
“To say we take violent crime seriously is an understatement. We are seeing some great results and have been actively taking dangerous weapons out of the hands of criminals who are intent on causing significant harm.
“While these results are good, we know we have lots more work to do. We must reassure Londoners that our capital city remains one of the safest global cities in the world. Manhunts and arrest enquiries will continue to locate further high harm offenders.”
Information can be provided by calling police on 101 or Crimestoppers on 0800 555 111. Crimestoppers is an independent charity. Calls are anonymous and cannot be traced.