A replica of a Red Arrows Hawk T1 aircraft has been installed in Downing Street to mark the centenary of the Royal Air Force.
The Prime Minister held a reception for personnel from the RAF, the Army and Royal Navy, as well as for veterans and Ministry of Defence staff.
In the garden of her Downing Street residence, personnel and the heads of all three UK military services gathered alongside veterans, civil servants and politicians including Defence Secretary Gavin Williamson and defence minister Tobias Ellwood.
The 101-year-old who joined the ATA in 1941, delivered more than 1,000 aircraft to the Royal Air Force - and chatted to Mrs May about her service.
During her speech to the 150 guests, Mrs May also said in an "increasingly uncertain world" the skill and courage of the RAF is "vital to the air and space power that allows the UK to respond quickly and decisively around the world". She added:
"Whether that is mounting immediate disaster relief or an evacuation operation, as we did in the Caribbean last autumn, fighting Daesh in Syria and Iraq as the second largest contributor to air operations in the region, or conducting a long range precision strike mission in a matter of hours as we did Syria last month - one of the gravest decisions I've ever taken as Prime Minister."
Guests included the head of the RAF, Air Chief Marshal Sir Stephen Hillier, along with the heads of the other two services and newly recruited trainees.
It was 100 years ago, on 1 April 1918, that the Royal Flying Corps and the Royal Naval Air Service merged to create the RAF - the world's first independent air service.
Mrs May said during the past century the RAF has "proved it is not only the first independent air force in the world, but also the finest", and stands "shoulder to shoulder" with the Army and Royal Navy to defend the UK.
The Chief of the Air Staff, echoed this sentiment and said the origins of the RAF lie in the Army and Royal Navy, and the formation of the RAF relied on those with the vision to deliver air power through a unified air force.
Sir Stephen Hillier said "strong political leadership brought that vision to life", adding: "But the military vision did not come from the RAF - how could it have?
"It came from the Army and the Royal Navy. I should point out the most senior leadership of the Army and Royal Navy at the time were not wildly enthusiastic about giving up their air capabilities and passing them on to a new service, but let's leave that to history."
He said the RAF "owes an immense debt" to those who were formerly in the Army and Royal Navy, adding the centenary could not be celebrated without both services for the foundations they laid.