Necause P40's were dubbed Flying Tigers by the chinese during the manchuko campaign. With the USA having very few forward operations from italy to help get supplies into china. Specifically china resistance to the Dragons(Zeros such, A6M4's IIRC). So it was Dragons versus Tigers.
The Flying Tigers sustained no casualties and came in waves dropping down on patrolling enemy jap aircraft. These were forced to fly low, because their mission was to spot caravans and/or shoot them up. Easy prey for boom and zoom heavy aircraft that would otherwise be caught up to.
Follow or not to follow a pair of P40's that dropped behind them to shoot them up. Miss or not, another wave was ready to come at them, so most of the time they were doomed. Keeping two, then one way into china open for food supplies.
They kept nearly 14 million people fed, that would otherwise starve. They are also the reason china likes us so much. They were hotshots and hard to handle, guys who wanted to prove something. They were sent there as either a joke or a punishment, or just to plain get rid of them. Little did the US air force know that china would be saving us from a 10 trillion debt, making 1/3rd of all our clothes and selling us billions of tons of material every year as a result.
The more you know...