The number of people turning to the charity Combat Stress has doubled since the recent events in Afghanistan began.
Defence Secretary Ben Wallace acknowledged that many of those who served in the country experienced things they will never forget.
It comes as an extra £2.7m of funding has been announced by the Government for mental health services for veterans.
The money forms part of Operation Courage, the veterans' mental health and wellbeing service, and will support former personnel facing unique challenges, honouring their dedication and sacrifice.
More than 15,000 people were evacuated from Afghanistan by UK troops over the course of nearly two weeks in Operation Pitting, which is believed to be the largest evacuation mission since the Second World War.
As the last British troops withdrew from Kabul, the Royal Navy's chief, Admiral Sir Tony Radakin, praised personnel and said their mission of stopping "al-Qaeda exporting terrorism" from Afghanistan to the UK has been "achieved".