A number of war memorials in central London have been vandalised with white paint.
The RAF Bomber Command Memorial in Green Park was splashed in white paint between 7:45pm and 9pm on Sunday according to police.
The RAF Benevolent Fund says it is the fourth time in six years the monument has been attacked.
The memorial commemorates 55,573 Royal Air Force Bomber Command personnel who died during the Second World War.
A statue of World War Two Prime Minister Sir Winston Churchill on New Bond Street and the Royal Marines Memorial on The Mall were also among other memorials that appear to have been vandalised.
The RAF Benevolent Fund says paint has been put on the Bomber Command memorial's statue of eight crew, its marble plinth and surrounding Portland stone.
In a tweet, Lieutenant Colonel Paul Smyth MBE defined the act "utterly tragic".
CCTV footage from the surrounding area has been given to police investigating the incident.
Chief Executive of the RAF Benevolent Fund Air Vice-Marshal David Murray said: "This is the worst example of vandalism we have seen at the Memorial and it is utterly heartbreaking to see the memory of all those brave airmen disrespected in this way.
"This despicable act took just moments but will take considerable time and resources to put right."
The charity estimates repairs could run into thousands of pounds. No arrests have been made.
It is not the first time the memorial has been subjected to vandalism, with there having been three other incidents since it was unveiled in 2012.
On two instances, spray paint was used to deface the memorial, resulting in expensive repairs.