On Friday Royal Marine Jonathan Crookes was killed in an explosion and Senior Aircraftman Kinikki Griffiths died in a road accident.
Sergeant David Monkhouse, from the Royal Dragoon Guards, was one of two soldiers killed in separate explosions on Saturday. The second soldier is yet to be named.
The fatalities mean the British death toll in the Afghan campaign since 2001 now stands at 322 and came as Afghan troops led a major operation into a Taliban stronghold.
The 500 soldiers were taking part in one of the first operations entirely planned and executed under Afghan National Army (ANA) command.
Marine Crookes, from Halesowen, West Midlands, was serving with 40 Commando Royal Marines when he died on patrol in Sangin in Helmand Province.
The 26-year-old reservist was described by his mother Sue Crookes as "a caring, thoughtful son, full of life".
His fiancee Danielle Davis said: "He was the love of my life. I can't explain how much I loved him but I am so very proud of him."
He joined the Royal Marines Reserve in September 2005 and volunteered to deploy to Afghanistan for his third operational tour in April.
Sgt Monkhouse, 35, from Aspatria, Cumbria, had previously served four tours in Northern Ireland and one in Iraq.
He died when his patrol was hit by a roadside bomb on Saturday morning in Helmand Province.
His family said: "For David, the Army was his life, second only to his daughter.
"He was the ultimate father and friend to Twinkle, more proud of her than anything else.
"His devotions were equally divided between his beloved Twinkle and his beloved Regiment, the Royal Dragoon Guards."
Senior Aircraftman Griffiths, 20, was described by comrades as a "consummate professional gunner" with "huge potential".
Wing Commander Paul Weaver Smith, Commanding Officer Bastion Force Protection Wing, said: "Senior Aircraftman Kinikki Griffiths tragically died whilst on vehicle patrol within the Bastion Joint Operating Base area of operation, just short of his 21st birthday."