Unintentionally handing over military hardware to the enemy - any precedents?

[Boyo_Jim]

In WWII, there were numerous instances by most all sides of combat aircraft getting lost and accidently landing at an enemy airfield.

[Really_Not_All_That_Bright]

@Gunslinger

Speaking of nukes, the US kinda accidentally gave the Soviets a few examples of the first bomber that could deliver them in the '40s when they were technically allies, the reverse-engineering of which which really helped them out a few years later.

Again, combat situation, so doesn’t fit the OP.