Is this the F-117A that they are referring to here?
https://www.theguardian.com/politics/2016/dec/30/margaret-thatcher-us-french-military-technology-national-archives-top-secret?CMP=Share_iOSApp_OtherAnother top secret prime ministerial file on Project Moonflower is worded in such an obscure manner that its so-called black subject is not immediately apparent.
“Dear Margaret,” a 1986 US telegram recorded, “I am delighted to hear that you will be able to see Cap [Casapar Weinberger, the US defence decretary] to discuss the special program I wrote you about … I look forward to receiving your reaction. Sincerely, Ron.”
In a top secret personal message, on which someone wrote in faint pencil “STEALTH”, an enthused prime minister wrote back after the secret meeting: “Dear Ron, I was immensely impressed by your splendid achievement: three cheers for America!
“I was also very touched by the generosity of the offer of participation which [Cap] brought. It brings home once again who our real friends are … I am so much looking forward to seeing you in Tokyo. With warmest best wishes, yours sincerely, Margaret.”
The offer of transatlantic cooperation on Stealth technology – which disguises an aircraft’s presence from radar detection – was one the MoD declined to take up.
An MoD letter in December 1986 to Charles Powell, the prime minister’s foreign affairs adviser, about Project Moonflower informed him that “Mr Weinberger has offered us a chance to purchase the current US aircraft but we have replied that we would not wish to actually buy hardware while the programme remains strictly black [secret].
“… [George] Younger [defence secretary] raised the subject very briefly with Mr Weinberger this morning … just sufficiently to test whether Weinberger is disappointed at our reaction so far. He certainly does not seem to be.”