During the days of the Blitz, the RAF relied on two primary aircraft for routing the Luftwaffe. these were the Spitfire and the Hawker Hurricane.
Both of these aircraft were surprisingly capable of holding their own against the Luftwaffe's Bf-109E series fighters. The Spitfire in particular went on to become one of the most effective and important aircraft of the war. Both of these planes' early variants were powered by the Rolls-Royce "Merlin" engine.
Though a fine engine, the Merlin suffered from a very major drawback. When pulling negative G-force (nosing down to enter a sharp dive quickly, in particular), the carburettor would flood with fuel, stalling the engine.
As the Bf-109 utilized injection type engines, they did not suffer from this same issue, and thus could perform evasive maneuvers that the Spitfire and Hurricane could not match.
Enter: Beatrice Shilling.
Shilling had an interest in engineering (and motorcycles) her whole life. By 1936, she had a reputation as a tinkerer, motorcycle racer, and genius. When she wasn't tuning up her bike and dominating the Brooklands race-track, she enjoyed a long engineering carreer with the Royal Aircraft Establishment. As promised by my headline, Shilling's fix for the "negative G" issue was simple, and odd in its simplicity.
The RAE Restrictor would manage the flow of fuel during negative G conditions, preventing the carburettor from flooding, and letting RAF pilots match a diving Nazi fighter with confidence. The component was also referred to as "Miss Shilling's Oriface" which sounds remarkably dirty to anyone who isn't British.
By 1941, every plane powered by a Merlin engine had this component installed, and later engines utilized injection like their Luftwaffe counterparts, or integrated Shilling's design. Still, this simple but brilliant fix made a huge difference in the RAF's ability to combat the Luftwaffe's assault on England, as well as their ability to push the offensive later in the war.