With new figures showing that the Ministry of Defence has spent almost £800 million fighting Islamic State over the past three years, Forces Network has taken a look at how that compares to other major military operations in recent years.
4. The Gulf War
The UK spent around £2.5bn as part of its contribution to the 1991 Gulf War.
Compared to later conflicts in the region, it was over relatively quickly and is seen as a success.
'Operation Desert Storm' took place over five weeks, five months after Iraq had invaded of Kuwait, beginning with an aerial and naval bombardment and then followed by a ground assault.
It ended with the liberation of Kuwait and decisive coalition victory.
The Pentagon has estimated that the war cost $61 billion, with US allies providing about $54 billion of that figure.
3. The Vietnam War
The devastating effects of the Vietnam War on all involved have been much-discussed for many years.
Britain famously stayed out of the conflict - a decision ultimately vindicated by history.
And while the human costs are well-documented, the financial impact to the US was also great.
The Pentagon has estimated that the overall cost of the Vietnam war was $173 billion (equivalent to $770 billion in 2003 dollars).
Veterans' benefits and interest would add another $250 billion ($1 trillion in more recent times).
In fact, during one campaign alone there was a massive financial cost to the US.
Operation Rolling Thunder, a sustained, eight-month aerial bombardment campaign, did $300 million damage to North Vietnam - at the cost of $900 million.
2. The War In Afghanistan
It's been reported that Britain's war in Afghanistan cost around £27bn.
Some estimates have placed this figure higher, though.
According to 2013 book "Investment in Blood", by Frank Ledwidge, the figure is £37bn - or £2,000 per UK household.
It's claimed this could have been enough to equip three Army or Royal Marine brigades and fund them for 10 years.
By contrast, the projected cost of the Queen Elizabeth-class aircraft carriers is £6.2bn.
The US, meanwhile, spent $686 billion during 'Operation Enduring Freedom' - although the long-term figure, when including the conflict's indirect costs, is likely to be much higher.
It's estimated total war spending will reach roughly $2 trillion, although even that figure leaves out expenses like interest costs, with America having borrowed to finance the war.
This alone could add trillions of dollars to the final bill.
1. The Iraq War
During Operation Telic - the codename for British operations in Iraq between 2003 and 2011 - the total cost of war reached at least £9.24bn.
46,000 troops were deployed at the start of the invasion, with the majority returning home by 2009 but around 150, mainly from the Royal Navy, remaining until 2011 as part of the Iraqi Training and Advisory Mission.
By contrast a 2013 'Costs of War' report from Brown University found that the conflict will ultimately cost the US $2.2 trillion, when including costs like future care for injured veterans.
Direct Pentagon spending amounted to at least $757.8 billion, which contrasts dramatically to estimates made just before the war about its potential cost.
Based on a shorter period of involvement, NBC journalist Tim Russert reported that "as American citizens [we should expect] that this would cost at least $100 billion" over two years.
The comment was made during an interview with Vice President Dick Cheney, less than a week before the conflict began.
These figures do not, of course, reflect the large human toll of these wars - from combatants to citizens of the war-torn nations involved.