End of an era
The shooting-down of a Syrian jet by the United States is believed to be the first air-to-air kill by a manned US aircraft since 1999.
Despite Hollywood blockbusters showcasing aerial dogfights, they have almost vanished from modern warfare.
In the 20th Century, skilled pilots who clocked up kills were often referred to as aces.
The US considers a pilot with at least five confirmed kills to be an ace - but no serving pilot holds the title.
"The era of dogfighting is largely over," says Justin Bronk, a research fellow at the Royal United Services Institute, specialising in combat airpower.
"After the totally lopsided kill-to-loss ratio attained by the US Air Force and US Navy during the First Gulf War, it is a very rare thing for regimes under attack by the US and its allies to send fighters up in defence - since they know how it will end."
In that war in early 1991, Iraq lost 33 planes to coalition forces. In return, they shot down just one coalition F-18.
That lesson led many countries to abandon competition with the US and its allies.
"Even in the latter stages of the First Gulf War, many Iraqi pilots chose to fly their aircraft to Iran to escape certain destruction - no light decision, soon after the brutal Iran-Iraq war," Bronk says.
During the Second Gulf War, Saddam Hussein "had most of his remaining air force buried underground to escape destruction rather than send fighters up".
And when Nato intervened in Libya in 2011 to aid the rebellion against Col Muammar Gaddafi, the country's air force did nothing to defend its airspace.
Most kills in the last two decades have been against enemy planes too far away to see with the human eye - which means technology often trumps pilot skill.
That gives the US a clear advantage.
It spends more on military technology than any other nation, has more aircraft carriers and deploys specialist ships with sensor arrays to aid its aerial fleet.
Faced with such a prospect, many air forces choose not to engage a technologically superior force - and leave their planes to conduct patrols or attacks on ground targets.
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